Financial talk

OK, so my husband and I watch our nieces 5-7 days a week for 7+ hours (sometimes days) and I love them obviously, but being kids they are expensive (food, fun, clothes, etc.) so I brought it up to my husband and he made his brother give him money for their expenses. I think my brother-in-law is mad now but it's like we watch your kids so much so I don't think it's wrong... And another thing, he like will go off to parties and other leisure activities and leave his kids with us...they are ages 8 and 2...I don't mind, but sometimes I want some alone time with my husband. Any advice as to what I should do? The mother is basically out of the picture so no suggestions involving her... We don't usually watch both at once, but the little one during the weeks and the big (and sometimes little one) one on the weekends.