well, i've managed to pass with all of my generations except for the one i have right now.
i'm pretty sure the instruments are not your problem.
i've changed my band's instruments a lot but i think you should let your tama plays his/her fave instrument.
i think you can let the two other band members play whatever you want them to play.
i practice my band (from the away icon) a lot.
i don't know why i do it but i practice until they get it right six times in a row or so.
the skill points MIGHT also help.
but maxing everything out doesn't mean you'd pass for sure.
one of my generations have passed with every skill around 400.
then the next generation, which is the one i have right now, has every skill maxed but still can't pass.
i practice with it just as much as i've practiced with all of my past generations.
maybe luck does have a role in this.
but who knows.
just keep practicing and hope you'll pass the next audition.
P.S. genders do not matter at all.