Kimberly, welcome. Sorry to hear about your problems.
First - if you have used real names I strongly suggest you change them to pseudonyms. There can be many reasons for this, not the least of which is the need for confidentiality. You need to have a place to vent when you need to, without offending people who you couldn't say these things to personally. For example, what if you had a really big fight with husband, or mother in law, and you posted about it here - and they tracked your online writing and read it? Or suppose at some later stage you had a problem with the school and said something about it here, and THEY read it?
And yet - you do need to be free to say what you feel here.
Now to your son - you need to have support. husband & mother in law have to back off, or step up to the plate. They can't have it both ways. If husband thinks you are doing a lousy job, then surely you would be doing a lousy job with BOTH kids. Are you?
Next - the current diagnosis is ADHD. Considering how much resistance there has been to ANY diagnosis, I'm wondering if it's more than ADHD, especially when you say that the lad is developmentally delayed, emotionally. If husband has been resistant to any diagnosis, then ADHD could be a compromise diagnosis.
And more - the various personalities and complexities involved here. The boy is five years old, which means his mother's death is still recent enough in husband's eyes (as well as mother in law's) for there to be some unresolved issues. You have a easy child daughter (I presume she's easy child) which could be rubbing salt into the wounds. SOmewhere at the back of husband's & mother in law's minds could be the thought that it is THEIR fault that the boy is having trouble. There could also be the thought that it's easier to blame you, than to accept the chance of personal responsibility. Plus the jealousy factor - your child is perfect, theirs is not. So if they can bring you down, make you feel less than perfect, then the glaring differences will not only be less obvious, but they will have produced a reason which can satisfy the world and assuage their guilt.
But they needn't feel guilty. ADHD, if that is what it is, is nobody's fault.
However, if they continue to get in the way of the boy getting the full amount of help he needs, THEN they will have to face the results of this later on.
How long have you been in this boy's life? You say you've been married a year, but how long were you with the family before that? However long it has been, it is highly likely that it is less than half the boy's life so far. In which case, how on earth can they justify blaming you for anything? What were they doing for this boy before you came on the scene, and why are they belong so obstructive now?
But we must get away from blame. This is not, and should not, be about blame. I do think a big factor IS about grief, complicated by ongoing grief for the boy's mother.
Here is a good link:
http://en.wikipedia.org/wiki/Kubler-Ross_model
I've lifted this from that link.
[The stages are:
Denial:
Example - "I feel fine."; "This can't be happening."
Anger:
Example - "Why me? It's not fair!" "NO! NO! How can you accept this!"
Bargaining:
Example - "Just let me live to see my children graduate."; "I'll do anything, can't you stretch it out? A few more years."
Depression:
Example - "I'm so sad, why bother with anything?"; "I'm going to die . . . What's the point?"
Acceptance:
Example - "It's going to be OK."; "I can't fight it, I may as well prepare for it."]
People go through the stages of grief at different times. People can sometimes get stuck at a certain point, or go back and forth between stages. Grief can be re-triggered for various reasons. It can be very complex. If people are at different stages of grief, for the same thing, they often are far less able to communicate effectively about it.
People also grieve for more than we realise. husband would still have some grieving to go through for his previous wife. Being married to you would actually slow this down, if he hadn't fully dealt with it before you met.
Then throw the boy into the mix - her son, which kicks him back to his previous grief. Now add in the grief he will have to go through (as will you) for the son he thought he had, and now has to accept that he never did have. All the dreams a man has over his son - all the wonderful things his son will become, the perfect human being, the genius scientist, the skilled doctor, the brilliant lawyer, the master craftsman - whatever his dreams, they have to come crashing down - unless he uses denial to cope.
The next stage is anger - and he's blaming you. Blaming you is connected to denial as well. But the blame, if it's being fuelled by the anger phase of denial, can be vicious.
There is another phase of grief I've read in other versions that includes guilt. And guilt is often masked by using anger as a tool. If either husband or mother in law feels any sense of guilt at all, for maybe some degree of attention they did not pay to the boy when they thought they should have, perhaps, then by finding someone else or something else to blame, they can deflect the sense of guilt.
What this boils down to - you all need help. But for husband & mother in law to admit that they need help is going to be a huge ask, because to admit it would also mean to admit that there are problems of this level. It's a lot easier to go on sticking your head in the sand and blaming someone else.
So where do YOU go from here?
Let's assume you're going to stick around. In which case - document as much as you can. Write down the boy's history, as far as you can determine it. Make a list of how he has been, keep a diary on his progress. List problems, but also list good stuff. And interesting stuff. Do the same for your daughter, so whatever happens, you have tis too, for her. You will value it. We never go to the trouble of writing this sort of stuff down, and we should. We always think we will remember it all; the cute sayings, the special days - but we do forget and it is a great pity.
The diary for your son will help log his progress as well as help pinpoint problems before they get too out of hand. And if you can use a form of this diary as a communication book between you and his school, so you read the teacher's daily notes and the teacher reads yours, it should also help a great deal (help the teacher AND help you).
IN the meantime, keep working with him, keep trying to determine exactly what he is dealing with and how he can be helped.
Have medications been suggested? How is husband with that idea? medications really help some kids, but not others. They were almost miraculous for my kids, even though ADHD is not he main problem.
Given your comment about social or developmental delay, I'd be wondering how thoroughly he's been checked out for Pervasive Developmental Disorder (PDD) in some form. have a look at the Pervasive Developmental Disorder (PDD) questionnaire on
www.childbrain.com and see how well (or not) he fits. Even if he scores as not having Pervasive Developmental Disorder (PDD), print it out anyway and take it to the doctor, to show the sort of things that HAVE been concerning you. The Pervasive Developmental Disorder (PDD) questionnaire is NOT officially diagnostic, because it just doesn't work that way, but it can give you a sense of direction.
You are doing amazing things for this boy, but you are trying to swim against the current. You need to stand up for yourself and not allow any criticism to be levelled at you. Don't wear it. Remember - the only ones allowed to criticise you, are the ones who are in there fighting with you. Anyone who is critical without also rolling up their sleeves and getting their hands dirty also, should put up or shut up.
If you could get husband to read here, it would be very good for him. It would also be good for your communication. But do not let him see any criticism of him here, because it would alienate him fast. He needs to be getting help from here, not feeling as if he is being targetted as the problem.
My husband lurked here so much he eventually joined the site in his own right. He reads just about everything I write here and sometimes if I say something he didn't expect or understand, we talk about it when he gets home from work. It is very easy to assume he understands, or knows, when he doesn't always.
Keep us posted on how you get on. Help is here, for all of you.
Marg
I guess I am here because I don't get support at home from husband, and my daughter doesn't get the attention she used to because difficult child demands sooooo much of mine. husband constantly critizes my parenting of difficult child although its obvious he's made significant progress. It hurts so bad, If I didn't care about his son I swear I would have called it quits if just for husband's attitude alone and interference/criticism from m-i-l. I joined this site to give/get support. It helps to know I am not alone. 
