Unless they have you on salary or retainer, tell them to go **** themselves with 20 songs in a week. And any real band knows you sometimes have to change keys to accommodate the vocalist(s). Sounds like a bunch of children who have no idea what they're doing. Just be honest and tell them what you can realistically do and they can take it or leave it. If you can sing and play guitar decently, you shouldn't have much trouble finding yourself a band.