Advice structuring partnership for deal

[Kaybreh Mathis]

Hello! Up until now, my husband and I have invested solo. We have a great potential property to brrrr, but it’s going to take $100k and we have $75k. My sister and BIL want to contribute the other $25k. However, he’s a professional painter but excellent handyman and can do lots of things like replace siding on house, lay flooring, etc. He could save us money by doing a lot of things that don’t require professionals like electricians or plumbers. How can I set this up fairly for us both? He doesn’t want paid hourly for the work, he wants that to be part of his contribution along with the $25k. I’m unsure how to figure out what everyone gets at the end. It’s not an easy 75/25 split if you factor in his labor. Advice is welcome! Thanks!