Get away from them, period.

The description of your family puts mine to a 't.'

Fortunately for me I don't literally have a family anymoreand I haven't had contact with either side of my family or about 40 years or better, so this isn't so much of an issue but now that I know I'm on the scale I can see in times past that on this issue as well as others, the people I call family were just as f** useless as a fart in a spacesuit.

In my case, I was ignored, but yours you need to make some sort of decision as to if you want to deal with these people which I would think that's tougher than you what I had.

It's total BS that blood is thicker than water, and it's a tough thing to come up against and work through but it happens quite often I think.

There are different names for spectrum disorders now, and aspergers isn't on the list anymore. It is just autism levels 1,2, and 3. I found out at a party while talking to my sister-in-law's best friend that my SIL "says my kid ISN'T autistic". Now, she's a secretary (basically), and has no kids, and knows absolutely nothing about autism except that her "boss's sister's husband's nephew..." (or whatever) is "really" autistic. This really pissed me off. To know that she not only thinks I made it up or something, but that she knows more than the 3 different places who diagnosed him with doctors who have PhD's and are experts on autism. So one day in a casual convo with her, I happen to bring up the processes we went through when my son was evaluated (3 times) and diagnosed. I went into great detail and probably bored her to death, but I gave a blow by blow account. Now, whether she believes me or not, I really don't give a shit. But to know that she's going around talking about my son and me behind our backs does piss me off. And like some commenters point out, they don't see the day to day issues that autists deal with. People love to be judgemental. A good way to approach it is to tell them that you may possibly value their opinions if they would make an effort to become informed on the subject of autism and it's different levels. And then offer to send them some links, or print some stuff up, or lend them a book or recommend some books for them to read. Or you could tell them that you wish you could have a conversation with them on the subject, but since they have no interest in becoming informed, it's pointless.

My son is ASD level 2, but I know what you mean. For a long time we dealt with family saying things like "He just seems like a normal kid to me" or "boys will be boys" - mainly because he was verbal and because they weren't around him much and only saw the meltdowns infrequently. At first I was really angry, but then I realized that this is what they wanted to believe. It made their world simpler and their family more normal.
I would tell them about my experiences and they would act sympathetic but ultimately come back with a story about how their kids misbehaved, as if it was just normal bad behavior.
One day, when my son was having a meltdown about putting on his shoes, after about 10 minutes it hit me - this is what they don't see. Of course, they don't see it so of course they want to think everything is ok. They love us and want everything to be ok. So, I took out my phone and filmed, with one hand, me spending about 20 minutes trying to get him calmed down enough to put on the shoe. I finally stopped filming and it took another 10 minutes to get the shoes on. Then, after he went to therapy, I sent the video to my family with an explanation of the context and explained that, some weeks, this happened almost every morning.
After that I stopped getting the comments. And my Mom started taking up for the issues we were having.
So, I guess I would recommend patience, understanding, and showing them in real time what you are going through. Certainly not ideal, but remember they probably are that way because they want everything to be ok.

I don't, why spend the energy if they are not interested