"Does your mom have brothers?"
Translation:У вашей мамы есть братья?
Yes, it is necessary. Otherwise the question will sound like "Is it brothers that your mother has?", as if you know she has some siblings, but you just want to clarify if they are brothers.
Ahhh, thanks a lot! I find this exact thing one of the hard aspects of Russian! :D
У твоей мамы есть братья? I cannot tell without context wheter duolingo wants me to use the вы form. So this should be right as well. But more context would also be nice. I like context. =)
The adjective must correspond to the gender of the noun. Мама is feminine, and so the form of "your" must also be feminine, and in this sentence, must also be in genitive - ergo, твоей or вашей.