That's kind of messed up that your younger sister would be saying stuff like this to you. Growing up, my younger sisters would never ever say something like this to me. Even my younger brothers would never say something like that to me. That indicates zero respect from you. Honestly, if you can't get respect from your younger siblings, how can you get respect from anyone?
I mean, we fought every now and then but to say "go suck a d!ck" at all times during the day is just absurd. This obviously stems from the dynamics going on in your family. Your dad not being assertive and your mom being abusive. There's no control figure in the house so the girl just acts however she wishes because she knows there will be little to no repercussion.