They probally have thread lock on them. I don't know what tools you have but they need to fit tight on those bolt heads or like you stated they are going to strip. I would take another box wrench and slip it onto the end of the other wrench to increase your leverage + spray them down with liquid wrench or the like. The other option is HEAT, don't know if you have access to some portable torches or if the yard would help you out but heat would help out a ton. good luck.
Yep,soak 'em with penetrating oil really good,go "shopping" for other parts and give them time to soak,and come back with a good wrench and some leverage and pull them.Buy a new wrench.It'll be worth the $5.00.