We are a small partnership with 4-5 properties currently, but we are growing and hoping to find a reliable lending partner that we can do repeat business with.About 3 months ago, we successfully completed a BRRRR deal where we had excellent numbers, over a 1.25 ratio at 75% LTV, our guarantor partner has an 800+ credit score, and we had no issues qualifying for the loan.

It sounds like you may not be cut out to manage rentals in which case you should probably sell.

How many flips in each area have they completed?  

Could/would Mom be willing to add you to title and you both sign for a mortgage, once renovations complete?

But it sounds like you should also balance your decision on what fits you and your families preference and style since you will be using it personally. 2.

Once you complete and rent/stabilize, you should easily be able to get into a DSCR loan.

Then they will take out leverage to complete the purchase of the second property. 

If I were the neighbor, it sounds like I'd be the only one bringing money to the table so you could get something you want.

You could force the seller to bring it up to code before the sale is complete as one of the contingencies of buying it, let them deal with it.

Quote from @Sean Barnebey: This is an interesting opportunity, and it sounds like you’re approaching it wisely by considering the numbers carefully.