If they both jointly own it, they sort of already are in business together. Unless your BIL is willing to sell his share (would you be in a position to buy it from him?) and assuming that you don't want to sell your share, I don't think there's any real way around that.
As 50% owner, it's not unreasonable of your BIL to get 50% of the PROFITS, but if you and your DH are to manage it, then your wages and costs will need to be fully covered, along with all of the other overheads and tax obligations, long before the level of profit can actually be determined.
I don't see how your BIL can object to you two running/managing it as he only has a 50% say in that anyway. He must know that it would be a huge amount more work for him, for no extra profit, were he to insist on hiring outsiders to keep it more neutral - and if he did, the hiring and staffing work would surely all be down to him, if he's the one wanting to be difficult when the two of you are already in place and willing to run it.
I think, realistically, he has pound signs in his eyes and likes the thought of having another string to his bow, but not having to 'lower himself' to actually doing anything for it.
It wouldn't surprise me if the shine soon wears off and, once he realises that it's more like a way for a hardworking couple to make a decent living rather than a bounteous magic money tree for all comers, he wants out anyway.
If possible, would you be able to put plans in place to buy him out should that time come - or, if you couldn't fund it, can you think of any friends who might want to do so? People whom you trust and know you could work well with? And if the latter, might it be possible for you to buy 10% from BIL and your friend/associate the remaining 40%, so that you retain the majority interest and sway?