There are a million different ways to do this but calling other owners is not something I had in mind.

So, let’s give a big round of applause to the RentRedi team for this incredible achievement! 

@Don Konipol Elevation, Palmetto and a couple of others do this for SFR owners.

Start by reading the Ultimate Real Estate Investing Guide: https://www.biggerpockets.com/guides/ultimate-real-estate-investing-guide/introduction2.

How do I solve this.

This may be the case to either leave cash in the deal or if you are unable to cover the payoff of the first mortgage, you may have to sell. 

This one will require moving several walls to reconfigure the space.

We didn't end up going this route on our remodel, but there were 2 designers we talked to who do everything virtually which saves a ton on costs.

Haven't found much resources on how to structure the deal whether to buy out partner's shares at existing basis (I believe this wouldn't be advantageous as I wouldn't get to mark the asset to market and lose out on depreciation) or open new LLC or S-Corp and buy out both partners (I would end up taking gain tax due to sale but would get new dep. basis).

I can point you to a free guide on tax delinquent property investing.