Am I wrong for this?

My brother wants me to braid my nieces hair but I feel like all my brother does is take, take, take and never does anything for anyone else. Literally, I bought my niece a $40 dollar gift and he told her that he got it for her. All because he wanted to be the first to buy her that gift. Like clockwork, on my nieces birthday and Christmas I always send her a gift. My son is two and he has never gotten him anything. Not even a baby shower gift. Y’all, he didn’t even tell my mom happy birthday on her birthday... he lives with her rent free. I usually let these situations roll off my sleeve but today I feel like telling him no. The thing is, I love my niece to pieces and I don’t want her taking it personal, she’s 8. I just got out the military so this is my first time seeing her in a minute. Btw, he told her to ask me so I don’t know how to approach the situation without it seeming problematic.

It kind of feels wrong because I’m being petty but at the same time I don’t want him thinking he could use me.

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