Feel free to draw on this but I don't want to put anyone else off responding more privately. I don't think it's feasible to ask them to join in directly so here's what I recall or infer. I'm still single (having moved out when I was 25).
I'm not sure I would have been offered a diagnosis before middle age (it was accepted enthusiastically at my work place). Except there are vague hints in my recall, which may have meant it was about to be broached when I was 10, but unfortunately, if so nothing came of it.
1 - I don't know, though I know my mum was wary of disabilities as she had had to take major responsibilities for others all her life (not knowing if it would reduce or add to her burdens, attract opprobrium by neighbours, etc). The others would probably have been moderately pleased if I'd been "decorated" with a label.
2 - i - older sibling, who was often out - didn't have any effect
ii - younger sibling - found me intermittently difficult (this has not been flung in my face, I infer it)
iii - my late parents - must have been worried sick when I was out of their sight, at any rate after I was about 17. Eventually I muddled my way through a college piece of paper and got a job a long way from them.
I do recall a phase when I was about 12 when I would get the whole family in stitches with my comedy routines (a passing phase, alas). There were a fair few times they could pull my leg about my plane spotting books, also Dad & I had fun on local history walks when I was older.
Before my elder sibling became adventurous, we used to write stories jointly. Later we would go round galleries together. There were a couple of phases of my going around with my younger sibling later on, which was more or less harmonious in itself.
Frictions around my objective failings would occur at home; worries would be caused to my parents when out (after 17). In short, many of my attributes were similar to or overlapped theirs, but I was gormless for my age, in many important respects.
I remember I became difficult for schoolmates to cope with when I was 17 (though I didn't see it then). Prior to then, I was not vivacious but not difficult either.
What happened when I was 17? Well it was following exam stress but there were also strange cultural attitudes that I got psychologically influenced by (not drugs) - those like now were unstable times.
After 17 till middle age, I was always stressed out so that affected how family could interact.
3 - grit their teeth and hope for the best, and laugh with me a lot (if they could).
I've hurried into this but I look forward to knowing why you're doing this; I should have waited!