takeiteasybuttakeit
Don't suppose there's any revenge I can take is there? Yes, as PPs have said it's living well and not showing any hurt. Revenge is a dish best served cold!
RE your son's school. I don't have a child with SN, but I have a DD at secondary school (yr 11) and I work in primary schools and part of my role is supporting the transition to secondary for the Yr 6s. So, fwiw, my opinion is that you should base your decision for your child's school entirely on what will suit him best.
Secondaries are VERY different to primary - there isn't that whole playground culture for a start. Parents are just in and around school as much.
As a parent, I might go to school on 4 occasions over the year (max). [I do go more, but that's in my work role when I'm supporting other parents] Typically you get one parents evening, and there'll be 2 or 3 events (like a winter fayre or something) and maybe a couple of performances if your child does music or drama.
As the parent of an SEN child, you might be in school more for meetings, but you won't see other parents and they won't see you.
Your child is likely to make friends and you'll rarely (if ever) meet their parents.
So EVEN if this 'gossip' follows into secondary, most parents won't be aware of it and if school gets to hear about it, they won't care a button.
Parents evenings are really hectic, so you don't get much opportunity to talk to other parents when you're there.
Honestly, I wouldn't worry to much about contact with this other family, and just concentrate on what's going to be best for your child. And this is what I mean about taking revenge as well, because if you end up choosing a school you think will meet his needs less adequately, then they've "won", haven't they. and you'll hate yourself if he doesn't thrive in the other school when he could have gone to this one.