Tired of dad always going with sister's side?

my little sister is a pain in the heiny. she cries when you accidently push her. (really softly) then she says she's going to tell on you. for ex. one time, at my old house, she asked me if i could get her a cup. i said ok, but first i wanted to see if she could actually reach it, (because she lies alot) she reached, and she was actually holding the cup!! i said "hey look, you can reach it. looks like you don't need my help." then i walked away. she said, "wait, i can't reach it!" i went back over there and told her that she really holding the entire cup. she told me she was going to tell on me. so she did. then when my dad came down there, she told him how i wouldn't help her. i said that she could actually touch the whole thing! but all he said was, "you guys need to stop all this bickering. i'm tired of hearing this all the freakin time! help her get her cup! next time be nicer!" then he went upstairs. it happens to me all the time. and i'm really tired of it always happening. one time, my mom and dad got in a fight. so my mom told my dad to stop always going on my sister's side.(because my sister back talks my mom) my dad said that sometimes my sister's replies are true, and she needs someone to stand up for her. tbh, to be honest, i had to agree with my mom. my sister always gets me and my brother in trouble for no enitre reason just because we didn't do something stupid that she wanted to do. and my sister always ends up with my dad on her side. how can i stop my dad from going on my sister's side all the time? all answers are appreciated.