So like am i an asshole?

Genuine question, lmao, My brother who has a daughter, she's about four sometimes they need someone to look after her since both parents has work, one has work from home and the other has to commute from home, so they need someone sometimes to look after their daughter,. Sometimes they call me and my sister to babysit, they do give small amount of money after hours of baby sitting, so like 100php(Philippines money) if we decline, our brother gets annoyed about it since we can't even look after our own niece. So he asked me again and told him i can only do an hour after he dropped off his wife from work then go home then i can go home after, but he did not like my answer of immediately going home, the thing is, I'm in my early twenties, i maybe unemployed but I'm still practicing to do interview or stuff for the job i wanted so like does that make me a bad aunt or sister? Beside, he only needs to dropped off his wife until he can get home while my babysitting my niece, i don't even need to stay long but typical guys who wants help of taking csre of their children so he can have time for himself