Looking for some advice on the following arrangement. 

Two partners are 50/50 in their business. The business currently rents but they're exploring the possibility of buying their own office space when the current lease is up.

Timing-wise, it isn't great for one of the partners, so the other partner will buy the building (with a third party investor, family) and rent-control the new office for the business, with an option for the other partner to buyout the family member if/when he's financially able to.

What would be the best structure or key terms for the family member's future buyout?

My initial idea was to do a full appraisal and refinance of the property. Let both the partner and family member cashout whatever equity and appreciation has been generated and start over, but it would definitely be the least cost effective since restarting a mortgage gets you back into the most expensive life-cycle of the loan.

The other option I considered was leaving the family member on the loan, and a separate agreement be made between the entering partner / family member with the building as collateral.

I'd be curious to hear if people have any concerns on the arrangements above or ideas for superior arrangements.