I would dread this, and am very sorry you have to deal with it. Since being diagnosed so far my parents have been supportive, but the rest of my family have been utterly silent on the topic: as bad a gossip as my mother is I know they know and yet... nothing, which is discomforting.
Anyway, do you think you could confront your family about it somehow, if not verbally then maybe write a note and leave it in an obvious place just describing how much their actions genuinely upset you. Some may accuse people with autism as unfeeling but the same often goes for those not on the spectrum, it seems. They may not actually realise you are taking their mockery to heart.
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On hiatus thanks to someone in real life breaching my privacy here, without my permission! May be back one day. +tips hat+