I want to chime in on 2., because I have a similar problem and there's some ways I've found to work around that. Maybe there's something you might like out of that. Because for God's sake, I don't need another scarf that I am not going to wear, my daughter doesn't need another plastic toy, and we really don't buy stuff at zalando and my family keeps gifting this to my spouse who owns like 3 t shirts and a sweater and likes it that way.
My favorite: Ask for donations in your name. Find a charity you can really get behind. My husband likes a buddhist foundation of a demised teacher, I like OVD Info. If the person who is gifting doesn't like the idea, maybe point out that it is tax deductible.
Ask for specific vouchers. If your folks are running out of ideas and are about to gift you an amazon voucher, try to think of something that you might use in your everyday life. Maybe it even is amazon; then set the same amount of money aside to get you something you really want or need and spend that money on everyday stuff. At least in Germany, there are services like Task Rabbit, where you can book a handyman to fix your window, install your heater, etc. This might be worth a voucher.
Ask for a voucher of time together. That's usually a stupid one (especially when you're autistic) because usually you can just spend time with people you like without a voucher. But sometimes it keeps them from getting you more junk.
Even worse for autistic people, but also worth a try - as kids we were encouraged (at school) to make voucher books for our parents with things like "1x taking out the trash", "1x vacuum cleaning" etc. I personally don't think these things should need a voucher, but maybe you can think of your own version. (Like, I shouldn't need a voucher to get one hour of gaming or for my spouse to compromise on what's for dinner, but maybe you're in a stressful home and this works for you.)
Obviously, self made presents or hand me downs. "Do you have something in your home that isn't of any use to you but you feel like I could still like it? I would love to have something that used to be yours and makes me think of you, while I also can give it a new, beloved home!" And everyone can glue a card sized collage.
Ask for things that you will consume. Cookies, good bread, pens, soap, whatever. So it doesn't accumulate.