I can relate somewhat; I'm not close at all to my mom and she always wants more than I'm willing to give. It took me a long time to feel comfortable saying no to requests that felt unreasonable. I used to say no but feel guilt or stress about it.
So I definitely think its a good idea to try hard to figure out what you are comfortable with, and what your boundaries are, and try to act in accordance with that rather than out of guilt.
But also try to keep in mind that all of your family may have done the best they could, even if it wasn't very good. Even if the end result was that you were neglected, it is probably (or at least possibly) fair to say that this wasn't their goal, which might make you less inclined to reject them now.
For me, I know it hurts my mom that I'm not close to her, and so even though it's completely reasonably that I'm not close to her, the situation troubles me, because I'd rather not hurt someone unnecessarily. This makes me more inclined to try to do thing for her, not because she's my mom, but simply because she's human. And because I'd rather avoid the possibility that later on, when she's not around, that I will feel regret over how I acted or over how little effort I made. I know I probably won't find the relationship that rewarding of itself, but perhaps I can take some satisfaction from having been kind. And I can try to change the dynamic to something more satisfying, even if it is only the satisfaction that I don't get as upset about it as I used to.
So I don't think you're obligated to your family, and I put no stock in blood is thicker...
And I don't think you should just go through the motions and pretend.
But I do think it's worth thinking about how you may feel later on, or even whether if you reframe the situation it might feel right to do something now - from your own choice, rather than obligation. If nothing else, it's worthwhile to have clarity about what you're willing to do, so you're also comfortable with recognizing the things you're not willing to do.
It may not suit you - I just reread your later comment about how being caring doesn't feel good at all - but maybe it's worth asking a bit why it makes you feel bad, and if it has to.
I don't think I said any of this terribly clearly, but i hope at least some of it makes sense.