Unfortunately, Barbara, in the circumstance you describe you are going to have to approach the other two and negotiate something. You do not have their permission to use their voices for a "for sale" CD. Perhaps they would just sign off, in which case a disclaimer would be called for. You should be able to negotiate something.

In general, the right advice has been given. Either of two methods could be used. In my band we split everything 5 ways, including the tasks to be done. In the next year I will do a solo CD. I will utilize some studio musicians who will be paid on a one time basis.