There are books around the place, I've seen some. Golden books... I suggest you go to your local library and ask a librarian for help.
I had a similar experience, I got pregnant with difficult child 2 when I thought I was past having any more children. There was a 7 year gap between the baby and the next child, and I was old enough to need amniocentesis. It was a problem pregnancy for me (although all mine were difficult in different ways). My mother did not "blow a gasket" but did advise me to have a termination; told me she didn't have that option in her day. I was hurt, because as I said to her, I was the youngest of 8 kids, the youngest by 7 years and was a change of life baby. Did she mean she would have terminated me if she had her time over? I made the mistake of confiding my distress in my eldest sister, not realising that our mother had for years lied about the true marriage year; my eldest sister was born only six months after our parents married. So both of us were upset by what Mum had said to us!
If relatives of friends "blow a gasket" then tell them to back off. This baby was conceived in love and will be born in love. You will cope, because people do. I coped, despite being disabled. I wasn't thrilled with having my chance at finally having some time to do my own things, blown out of the water, If I had known difficult child 3 would turn out to be autistic - I'm glad I didn't know. But he is an amazing kid, and there have been aspects to parenting that I have found thrilling.
Another interesting point - by the time we began to have problems with difficult child 3, I had already learned a lot with the previous three. And when difficult child 3 was diagnosed, it also pointed the way for difficult child 1. If it hadn't been for difficult child 3, I doubt difficult child 1 would ever have been diagnosed.
Your kids are much closer in age than mine. easy child was in high school at 12, when difficult child 3 was born. I remember difficult child 3 attached to her as if she was his mother; when she saw a specialist about headaches when she was 14 and the toddler climbed up onto her lap, the doctor asked easy child if she had had the headaches during her pregnancy! Nope, that's my kid; he just thinks his sister is his mother...
You have two boys. Maybe this time a girl?
And maybe this time you can enjoy the pregnancy and the baby, knowing so much more this time.
Congratulations! Just do what we did, tell people you have decided to raise the national average IQ.
And if anyone says, "How did this happen?" just tell them, "In the usual way!"
Marg