Switch lenders, get a new appraisal.

The anticipated value after these improvements is estimated to be between $550,000 and $650,000.I only have enough cash to put down 10% if you know of a lender or private money investor who would be a good fit please reach out to me directly or comment below.This will be my 4th BRRR property. 

Will any lenders hold multiple lots for collateral and release them for building maybe 3-4 at a time?  

Once you have your team: Realtor, GC, Title Co, Lenders, etc.. and you feel like you trust them, then move forward from there.

You will be pulled into the lawsuit between the lender and the borrower.

I'd love to get in touch with a mortgage lender to see what do I need to get approved for this kind of loan.

If it ends up being an expensive or time-consuming repair, you may be able to get bids and have the seller escrow 1.5x or of the bid cost to do the work post-close with a signed agreement and lender approval.  

I've been using FCI Lender Services for about 5 years and find them to be very investor friendly, especially for newer/smaller investors. 

Don’t be afraid of rejection.

The lender would have had an appraiser issue a opinion of market rate rent for the apartment on your duplex so that's a start on what the rent should be.