Firstly, well done for persevering and trying every avenue you thought would get you the data you needed.Most would have caved earlier and handed out there hard earned cash for old, saturated leads/records from the same prominent platforms which dump them pretty much when they receive them from either 1).the same large brokers AFTER the county has listed them on the county website or, 2). from the counties themselves directly AFTER the county has listed them on there own website, or, 3). from data scrapers on Upwork/Fiverr who scrape the data from those same platforms AFTER the counties/brokers sell those platforms the data being scraped by the freelancers.Anyway, rant aside you seem to of made the same mistake i made when I first started branching out away from providing leads to my original couple of clients i got from Upwork who wanted me to scrape data from court records in FL for pre FC leads.Simply, I didn't know where to look for the information I needed in states outside of FL.FL only allows the judicial route to foreclosure so I only needed to know/find/scrape the data from Lis Pendens documents for counties they requested.

You can always get MLS data many places.You be the investor, let the realtors do their jobs.

Could you gift the down payment to your mother in law so she can buy it and then transfer title to you when your house is done?

I would still work with a title company on this and let your lender know (if you have one) of the name change and what you are doing so they do not think you are selling the property.Another option would be to create a living trust for estate purposes and transfer it into the estate.

Upon her passing, the 401k interest was transferred to me into an inherited IRA account at the same servicer.

+1  Real Estate Investing Data and How-to Guides - This here shows that you can filter to Multi family but I don't see it as an option as well.

And if your selling NON mls props its hard to run data..

Looking for guidance on options. new builds aren't hard to finance and I would argue they are preferred to existing fix and flip loans, especially if you have experience. banks look at your experience, your builder's experience, loan structure, permits, etc you need to get an experienced builder familiar with advanced underwriting and negotiations with local, regional, and national lenders. in columbus we do ground up construction for clients at a 20% discount so they can BRRRR out of the new build with equity and we have pages and pages of data on what we build and why and it's all supported by market statistics. 

What percentage of sellers are still contributing in some way, do we have data or knowledge of this?

Too many stories of hacking to get at wire transfers, etc.