What should I say to my bandmates?

Ok well I'm in a band with my best friend. We haven't played a show
yet but my friend called me saying that he's gonna try getting someone
to book us in the next week or two for our first few shows. There's
alot of creative difference between me and the rest of the band (the
drummer and keyboardist expecially!!) My best friend and I do like
similar bands (KISS, Ramones etc.) but to be quite honest with you, I
hate the songs he writes. They're just boring. The band sounds so
f**king generic as well and there's nothing unique about what we do.
Our drummer (MY BEST FRIEND'S SISTER) and our keyboardist (WHO I DON'T
EVEN THAT WELL) are the one's who make the band sound as horrible as
they do. It's too hard for me to convince my friend (singer/lead
guitarist) to kick his sister and a good friend of his out of the
band, so the only thing I can do is leave. I just don't really know
how to tell him properly. I've hinted to him that I don't like the
band and many things about it (the name, the genre, the other band
members) but I'm having trouble on what I should say or how I should
say when I tell him that it's time for me to leave the band. And I
don't want it to ruin our friendship either.
OH AND ANOTHER THING! My friend told me that when the band 'makes it'
and gets really big, he plans to work with Justin Bieber and do a rock
record with him, which really pissed me off.
My band's influences: Coldplay, U2, Muse, Justin Bieber.
My influences: Ramones, Misfits, Guns N Roses, Metallica, Black
Sabbath, KISS, Alice Cooper, White Zombie, Slayer, Iron Maiden, Motley
Crue, Sex Pistols.

See the problem??