My son has always been different but he wasn't diagnosed with Asperger's till he was 22. I modified my home for my ADHD child and it worked for him with exception to his anxiety but basically he still had issues they, my family, didn't acknowledge.
I've learned that they can't be a support for me or him surrounding what he needs and I've had to develop other avenues. I started a group in my area and now we have great support with other families experiencing the same types of things. It's been a life saver for him and for me.
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I can understand exactly what you are going through. It can be so frustrating. It took a lot, and I mean a lot of educating my family/in-laws to make them understand my son. I would explain the different reasons of why he was behaving (and it wasn't bad behavior, just not NT behavior) due sensory issues or being overwhelmed by the amount of people at a family gathering etc. It didn't happen overnight, but it did finally happen. They don't question well why is he in the other room when there are 25 people over etc. You have to be persistent and to be honest, if they can't deal with it, then I'm sorry to say then I would not be around those adults. I know other families who have had not speak to relatives b/c they just didn't get it and would make the situation worse. They don't like it, but it really didn't help their child out. I really hope you can explain to them why's and not have to chose the later.

My son is 32 and my family still doesn't get it. I think that some families are open to hearing it and other's aren't. I just don't leave my son with anyone other than people that are our support people and when I'm with my family I make sure that I'm watching how they interact because some of the things they do last weeks and if I can circumvent it before they finish the craziness they do it stops the persevering for my son. It's just not been worth it to me to get them to understand after all these years.It's very frustrating but once I learned where to put my expectations it's become easier.
The cousins and people his age get it but the older adults don't. The people his age though try to get him to do what they do and that doesn't work either. Like you said, my son looks normal but functions all over the place. Somethings he's very mature about and other things are like a 15 year old...

Speaking of disciple. 1-2-3 Magic was a lifesaver for me.

Please be respectful to my Mom and Dad if they let me "stim" for a while as
they know me best and what helps to calm me. Remember that my Mom and Dad have
to watch me much more closely than the average child. This is for my own
safety, and preservation of your possessions. It hurts my parents' feelings to
be criticized for being over protective, or condemned for not watching me
close enough. They are human and have been given an assignment intended for
saints. My parents are good people and need your support.
Holidays are filled with sights, sounds, and smells. The average household is
turned into a busy, frantic, festive place. Remember that this may be fun for
you, but it's very hard work for me to conform. If I fall apart or act out in
a way that you consider socially inappropriate, please remember that I don't
possess the neurological system that is required to follow some social rules.
I am a unique person--an interesting person. I will find my place at this
celebration that is comfortable for us all, as long as you'll try to view the world through my eyes.
Author, Viki Gayhardt