An LLC resolution enabling the LLC to manage property that is committed as a capital contribution (from a managing member's property) would be another solution, but again check with an attorney in your state. 

I know one of their Directors, Eric Robbins, and he can likely provide you with a number of ideas plus actionable solutions from Semble. 

Do you have any other solutions to that?

You're communication with the seller and building rapport can put you in a position to propose any or all three suggestions to find the right solution for the seller. 

I really will have to come up with a creative solution if I cant remove the stain as the rest of the house is a few days from completion and the shower surround tile/glass door etc are already in place.

If you want a cheap & dirty solution you can take it down, paint gorilla glue inside all the splits, and pull the door back together with 48" bar clamps.  

or what is a better solutions?

If you can get a bank loan, that is a good solution.  

Otherwise all income and expenses will be in proportion 25%/75%I am looking for the simple and cost effective solution, which could keep each other accountable.Kyle

I'm just not sure my comfort level would be very high with that solution as I'm just jumping into this.