Common sense says that they are all parents' children, and the palms of their hands are all meat. There is no preference for boys in your family at present, so why are they a little cold to you but enthusiastic about your sister's family?
Personally, I think the reason may be that long-term separation has led to emotional alienation.
You were given away as a child and never lived with your parents. After a long time, their feelings for you are no longer so warm; On the contrary, your sister has been living and growing with them, full of natural feelings.
But there is still a problem. Many cases show that in many families like yours, parents are very ashamed of their lost children. After all, they have not fulfilled their parenting responsibilities, and they will double their compensation for their children's guilt.
What happened to you was just the opposite.
Maybe there are other secrets in it.
But I want to say that after all, they are your parents. If you are unhappy, you can communicate with them directly. Otherwise, if you keep silent, it will be bad for you and them in the long run.