So recently this one girl has been showing big signs she likes me, I know for a fact she does, I'm weary of dating her for multiple reasons: 1) I'm good friends with her brother 2) there's a definite age difference(I'm older) and 3) the big one, I really like another girl that Im confused whether she likes me. Ive flirted a bit with the girl that likes me and I feel I'm in too deep to the point I don't want to hurt her by backing out and just being friends, but I feel that's the only option.

Any help with what I should do with this situation would be much appreciated

The best thing you can do for her is tell her exactly how you feel, that you just want to be friends. Don't lead her on by not discussing this.

Tick

I would say stick to the girl you like,3 years makes a big difference in maturity if the younger one is a teenager.

Be honest with her,or just back off with the flirting.