It sounds like you've had complication after complication making even more a mess of things for him. It's really hard, having to deal with so much - hard for him, hard for you.
You've raised a daughter who you don't mention having problems with, so this isn't bad parenting. However, it could be that your parenting method, which would be quite OK for most kids, is making him worse. it happens to all of us. Not that you're doing it wrong, only that it is wrong FOR HIM. And how could you know?
because of what he's been through, you've already had to learn to think outside the square. This is good. Because from here, that's what you need to do.
Look at how you try to manage discipline. What is your method? And the big question - is it working?
If it is not working, then you need to change it.
But what to? Not so easy.
Here's where I suggest what many others on this site will also suggest - a book that has helped many of us is "The Explosive Child" by Ross Greene. Look him up, get it out of the library, read anything on CPS (Collaborative Problem Solving) which is the method Greene describes, then see what you think.
The kids that bring us to this site are many and varied. Their problems are also many and varied. What is wrong with my kid is not necessarily what's wrong with yours. But that doesn't matter - some things don't change. Our kids underneath generally are good kids, trying to do the right thing but often feel completely lost and unable to explain what is wrong. Then they get angry, frustrated and problems escalate. We punish (and, looking on, it all makes sense to us at the time) and often the child is too angry or not really in touch with what we see, for this to work the right way; instead, the child sees us punishing because we're bigger and we can.
Ross Greene's book helped me get in touch with what my son was feeling. Once I could understand him, it was easier for me to work at his level and begin to help him from there.
They are children - they are still trying to understand the world so they can fit in. We are adults, we are supposed to be wiser, but we need to meet the children where they are, and show them in ways they can understand.
I'm not implying your son isn't bright enough to work things out - this is not a problem limited to 'slow' kids at all.Far from it. My son is incredibly bright, but he's needed a lot of help to show him how to fit in.
It's just that some kids, for a whole range of reasons, need more hep than others, in a lot of ways. Which ways depend on which kid. The parent has the best chance of knowing where their child is coming from. Once you have that key, you can begin to open the door for them.
Welcome to the site, sorry you need us but glad we're here for you.
Marg