Need advice to run farmers market with other family. How to split profits?

I need opinions on this. We have some vacant land and because of medical issues, we've been looking for someone to start a farmer's market on the land. We found a couple that we're interested in working with and we're going to talk to them in more detail next week about it. They seem very eager to really build this into a neat place that people will want to come spend the day at. Our thoughts are that they would charge vendors a fee to set up there to sell their vegetables, flea market things, craft/arts. Say this fee is $20 a space. We felt that if we split that fee 70% us and 30% them,....that would be a good split. We would pay for insurance, porta potties, web site domain hosting, we'd get the permits, and take care of the land(mow) and improve the land(more needs to be cleared as it expands). They would handle advertising and getting vendors and dealing with the vendors that day. They could also sell their own things there. They had mentioned had we considered starting it as a non profit for tax purposes. I'm not sure how they meant this(I'll find out more next week). We pay the mortgage on the property and also the taxes. So say there were 30 vendors at 20 a day to start. They would earn $180 for that day and we would get $420. Then I thought we would both handle this as a sole proprietorship and pay taxes that way. This is Illinois by the way. Can you give your constructive opinions on this? I also feel they might want some protection. In other words, they build this envroment, and I don't want them to think we'd take it over once it'sflourishing. We have no interest in that type of thing and we're not the type of people to screw anyone.