I've only one bass right now, and unless I'm gigging, I don't see the point in having more, fretless/upright maybe if you like that too but anything else is just obsession for a bedroom bassist. If he's just playing at home and not doing anything else with it, you shouldn't put up with it, unless you've got an endless supply of space and money, but I expect you don't lol, in which case there's always gonna be more important, more constructive things to spend money on.