I don't want to be near my super tight-knit family
Why don't you want to be near your family?
They're too much sometimes. I need some distance.
You can spend time away from them If you want. Everyone needs some alone time.
I'm not going to tell them I'm remotely autistic. I've enough problems at home as it is.
It's totally natural to want time alone and you should feel fine about that. If you're autistic, you might want to talk to them about it, unless you think they will treat you badly as a result.