Family expects me to buy clothes for niece?

My sister and her family is very poor and I’m a grad student and I’m doing pretty good. I have on many occasions bought things for her kids and gave her and her husband money. But the kicker is my sister doesn’t even like me and my niece doesn’t like me either, also my sister husband. I only do this because I’m a kind person, but I’m not happy helping people who do not like me… right now my niece has no money for school clothes and they asked me to give her some of my old clothes or buy her a few things. The thing is I don’t want to and my niece talks back to me and her grades are straight F’s! What should I do? My boyfriend says stay away from those people. I just feel guilty because They are family, but they don’t treat me good. What would you do?
Family expects me to buy clothes for niece?
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