You need to sit down with your band and set one time a week that everyone keeps free no matter what for rehearsing, or if you can't rehearse, then organising gigs, promo, whatever.
Once you have a set time every week that you can plan around it makes the whole thing much easier. If the people you're playing in a band with can't committ to a regular rehearsal then probably you should not be in a band with them if you are at all serious about it.
As far as collaborative writing goes, I'm a fan of someone writing a tune on their own time, then bringing it to rehearsal to workshop with the rest of the band. Rather than saying "This is how the song is going to go and that's final" it's more like "here are the chords and can we try it like this and see how it sounds" and they will probably go with some stuff, and write new stuff as well. If after a while you find you completely disagree with everything they do to your songs, then maybe consider not being in a band with them also.
Bands are like being married to multiple people. You need to compromise on stuff if you're going to keep it all together.