Where are you and the kids (rightful owners :-) when he's loaning this good stuff out? I think maybe you could make a case that since he does a lousy collection job on some loans that he's only allowed to lend out his own stuff, not "joint" or the kid's stuff or yours and he has to let you know when he's loaning something out (so you can bug him to get it returned a little faster when there's a chance it will be).

I'd give him good marks for sharing and helping others but he doesn't quite have the financial portion of the partnership down well enough to be allowed out on his own? LOL