the way we receive or ask for gifts
My family--my mom and maybe my dad excluded seem to think that when you receive a gift you should always "like" it. And when you would like a particular gift, you should not ask for it unless someone asks you first what you want.
I had been giving gift suggestions for years and did not know I was offending them. I was doing quite poorly psychiatrically for a while, and fianlly, when I was doing better, my brother-in-law took me out to lunch and said (in a nice tone of voice) about my emails with gift ideas, "we got to tell the kids this, too". To me, it seemed that taking me out to eat to tell me this made a far bigger issue out of this than it should have been. I can see, however, that maybe they thought it may be better that way.
Then, when I get a gift and feel I have no or little use for it, they expect me to "like" it, which seems like nonsense to me--either you like it or you don't, or you pretend to like it.
They get very upset about this kind of issue. My brother once said something to the effect of, "when you get a gift you don't want, you take it and hide it away". My question would be, "Why?"
Once he said to me, "How would you have felt if Jacob [my youngest nephew] did not immediately start playing with that gift you gave him?" My response would have been (but I did not answer because I actually thought at the time it) that I did would not want him to ACT like he liked it; if he did not like it, I would have felt somewhat bad I had given him a bad gift. Personally, I would not have liked to "act" that I like a gift when I really don't--seems dishonest.
I don't know how to approach this issue with them.
It is hard to understand, and it might not make sense but I think it might be best to play along. Some people feel personally hurt if a gift isn't liked - they feel it is a reflection on their taste and their choice. So if it is clear that you don't like something it can feel like an insult. If possible just say 'Thank you very much, that is a very nice present'. I know that feels like a lie, but you are thanking them for giving you something (whether you like it or not) and saying it a nice present isn't really a lie either because it probably is a nice present, just not for you.
As to asking for things - that is more tricky. I don't like surprises at all, and when I was a child I used to get so overwhelmed at Christmas that I would have meltdowns and ruin it for everyone. Luckily for me, my Mum can't keep a secret so she tells me what everything is so there are no surprises. I think that if someone says 'Could you give me ideas of what you would like for Christmas' then it is polite to mention a few things that you would like so they have a choice. Sending suggestions when they haven't asked might be seen as rude.
Personally, I think your family are putting you in a very difficult position by telling you that you have to pretend to like what you receive, and yet not allowing you to tell them what you want! It does seem like a very illogical position to me.
The only solutions I can think of is if you try again to explain to them that you find this very difficult, and perhaps suggest that gift vouchers might be a better option - some people are happy to have the pressure of choosing a gift taken away. If that is not a possibility could you speak to your Mum and Dad about this? Perhaps you could give your suggestions to them and then they could mention to your sister a few things you might like when the subject of Christmas or a birthday comes up. That might feel very patronising to you, but it would take the pressure off you.
It is because of issues like this that I'm not a fan of present-giving occasions, it's all such a social minefield.