Whose name is on the deed when purchasing? If there is lending, whose name is on the loan(s)? When a project sells, whose name is on the 1099-S? There likely is some project insurance; whose name is on the policy?

If this all ends up being one of them as the "money man" then what you have is a Schedule C sole proprietorship with a subcontractor, and that's easily resolved. You mentioned they split the proceeds, so that amount is the 1099-NEC for the subcontractor. Make sure you follow up with the 1099 process. They're late.

The projects that span across a year end are not expense; they are asset as work in progress. Make sure you understand how to track construction accordingly, and the tax impact will be pretty much what they agreed to among themselves.

This is totally ignoring things like worker comp, worker misclassification, and doing things correctly, of course.