band dillema

my friend wants me to join his band despite the fact that im a percussionist (i play tambourine and cymbals, plus they already have a drummer). he also wants me to do backup vocals even though i've never really sang in front of him since im nowhere close to good at it. it isnt like i dont want to join, it's that i don't know the people in the band except for him and i would have to rely on my friend for transportation and such. my anxiety disorder makes it hard for me to leave places and also hard for me to perform onstage.

he also said that i could play guitar but that's stupid because yes, i have a guitar, but i can't play for shit, and it's also broken. i've also already kind of joined my cousin's band(?) technically, it's not a band yet but i don't know if you can even be in more than one band without having issues/drama.

i doubt my nana would let me join any band, let alone with people i don't know, and especially won't let me play at gigs.

i'm completely lost on what to do and i haven't gotten a clear answer on whether im in the band(s) or not.