I'm glad the neuro was positive, you sound upbeat too.
After my DS's MRI on tues we found out he has a heart valve issue, not the same as your DS though.
How old is your DS4? I know not all cases are the same but we were told that as long as he did things in the usual order, albeit delayed it was fine.
On his first developmental assessment (at 20 mths) he was between 10-14 mths behind - average 50%. We have worked hard with him, Portage, Physio, hannen, Makaton and exposure to many diff experiences. At last developmental tests he was still 11 mths behind but at 34 months that is only 30% = he is closing the gap. He was 3 on Sunday.
Your boys are lovely, all blonds! What a lovely lifestly you have, do I remeber that you live in the SE?
Let us know how your blood tests get on, I've never had any info from any of ours!