As far as covers go, I have a policy that I wont go into a rehearsal studio with the full band, unless everyone has done their homework, fortunately with my current band, the 2 singers (3 if you include BVs) even get together without the rhythm section to sort parts / harmonies, also the guitarist and keyboard player do a lot of "who's covering what" stuff also.
It works wonderfully, but I know I am lucky.
My only other gigs are deps, so its similar slotting in also
Couldn't go back to "whats the chords please" sessions, its just not worth it
Of course thats the beauty of a covers band
--
Id suggest you suggest the above approach to the band before giving up and give them a chance to get into it, that is of course if you think its worth it