I think this Miss Manners article was outstanding & it applies to kids/people/teens/steps/bio's:

Dear Miss Manners: The day after Thanksgiving, my aunt e-mailed my whole family her children's Christmas list, noting from which stores the children will accept gift cards and including all their gift wishes.

Is it wrong of me to be offended? Her children are almost 15 years old, and I thought them too old to be demanding gifts or making lists at all.

Gentle Reader: But they have had nearly 15 years of training in this method of demanding that others give them what they want, and it seems to have worked so far. Why would they quit?

Children's wish lists cease to be cute when they no longer believe that they are confiding in Santa Claus. Miss Manners is not even sure about then.

It seems to her that receiving presents should be the opportunity for them to be taught to show gratitude, not to systematize natural greed. And by this system, the adults have no chance to expand the child's horizons by interesting him or her in something new.

Perhaps it is time for you to change tactics in your presumed goal of showing affection for your young cousins. Instead of fulfilling their shopping demands, you might plan some sort of visit with each individually, so that you will get to know them all better. If they are responsive, you will be able in the future to select presents for them yourself, based on your understanding of their present and possible future interests.