I know you can sell brahmins to NPCs, but I don't think you can sell/give a Brahmin to another player. I know that it would be quicker if I could simply give one of my brahmins to another player than having to give them rope and make them do it themselves. I know that catching a Brahmin is easy now, especially since they don't attack you on sight, but this could make it a little easier.
Maybe one of the dialogue options would be to say: "Brahmin, you should now obey ____ from now on" or something like that.