It's simpler if one person is the band motor. More than likely not everyone wants to do the bookings, which is the hard part.
The guy who books the gig puts the entire sum in their personal bank account (a separate account from their personal finances). This person pays the musicians for their services from the total funds received from the client. This person also takes a greater share of the total than the other musicians to compensate for the sales, marketing or other expenses s/he wants to incur. This person isn't required to disclose the total fee charged to the client to the band, and shouldn't to avoid hard feelings. S/he simply offers the musicians the gig at a price they will accept and the business/band motor can afford. If they refuse, find a sub and grow your options. A hassle at first, but eventually you hit a threshold where everybody can be subbed to the point you don't have to check availability for gigs -- just book them and fill them with able musicians. At the end of the year, report the gross sales, and subtract all your equipment and musician expenses. The surplus is your net income you report on your personal tax return.
At the end of the year 1099 those who earned more than the contractor's threshold of $600 in 2018.
Buy the PA and other equipment yourself, or Frankenstein a system with the other members, and don't fall into the trap of paying people who haul parts of the PA more than everyone else. Don't expect others to drop coin for band equipment, as they may want compensations. I don't, and no one complains. Help people at the gigs haul the stuff though, to mitigate the pain.
This is simple. If someone gets mad, leaves, quits, dies, moves, etcetera, you are still in place and can keep on a-bookin'. You have musicians, equipment, and a surplus in the bank to cover various expenses. And the band members who aren't business minded can just show up and play -- what most want to do anyway!
I would avoid a complicated agreement where everyone has ownership and you have to make decisions as a group on the business end. Just offer them what the gig can afford to pay them after compensation for your trouble and your expenses. But be fair! If you get a good paying gig, share it generously with the musicians. I even play for free sometimes if we don't have much going and I want to keep the band sharp. But I broadcast this to everyone, along with the expenses I have to pay (insurance, for some gigs, repairs on broken equipment, web hosting fees).
I used this method after I found a) no one wanted to do the gig booking work to help me b) they didn't answer email or approve reasonable band expenses and c) I started feeling like a doormat for the band. They controlled the repertoire, demanded high rates of pay, etcetera, while I sat unfulfilled in my requests for songs to play, and my lackey status in the band.
No more. This system has me feeling fairly compensated. I know the rates various musicians will perform at, and I invite them to perform at gigs accordingly. I have four piano players, three bassists, two sax players, a flute player, two guitarists, 5 drummers a drumming and a partridge in a pear tree. Plus a big band to draw on in case all these cats are busy.
It's heaven. And with an ever-shifting group of musicians, you end up standardizing the repertoire and not having to rehearse much.
Interpersonal problems are almost non-existent. And when one cropped up recently, all it took was a stern kind of warning and the two guys apologized and stopped their objectionable behavior recently. When you are paying people, acting more like a booking agent than a peer in a band, you get privileges that, in my case, make me want to keep on being a band leader.
