@Rud SevHere is a start:https://www.biggerpockets.com/forums/51/topics/839015-are-sy...https://www.biggerpockets.com/forums/51-tax-legal-issues-con...

We thought about hiring a lawyer but the legal fees were expected to be in the range of $10k to $15k and would have taken months (if not years).

Are you aware of city of San Diego rules regarding converting existing legal space to ADUs?  

Can you buy a house with a legal suite?  

If you need financial help, ask under the "Finance, Tax, and Legal" forum.

I was interested in the finance and legal aspects of operating a multi-state buy and flip equity fund.

It will also require extensive networking to raise funds from other, legally, to buy at scale.Recommend your plan be more realistic with a goal of 10 years for your real estate to be generating enough cash to live off - and even that may be a bit optimistic.How to grow?

Should I continue mediation or pursue legal action (considering the time and costs involved)?

Examining “risk” we see two different additional risks.  

Get a real estate attorney with some experience in the matter and have them use a PSA and back you up legally, perhaps even help with some due diligence.