I offered 508K on a duplex and offer was accepted, one unit is already rented for a year (below market, we could get more when lease is over) and the ROI and strategy to househack for a few years is perfect for my family to start-off our investing journey, we would be saving a lot on rent.

It is my firm belief that the sooner you accept this fact, and come to terms with it, the sooner you have an actual chance of becoming successful.If your born skill is to drive for dollars, and you are SICK behind a steering wheel, and you decide to do door knocking, you will FOR EVER be struggling, no matter how good you are at knocking on that door.

I could probably live with that, but even with his desire to help us out I can’t imagine him accepting $200k under market value for the property.

Your financials may be able to offset a lower than acceptable DSR (property needs rents raised), but that depends on the lender.3) Can't help4) Ownership percentage, who is managing member and thus has authority to make decisions and sign for LLC, what happens if a partner can't make capital call, etc all usually pretty standard.

The concern could be that you are attempting to coerce them to accept your family over another family or individual who may or may not be in a protected class.

At that point you are free to accept the 2K, deny them or appeal the decision. 

If you're offer is accepted you have at least 2 opportunities to see all units before closing, during your: (1) inspection, and (2) final walkthrough right before close.  

Have you been making offers and they aren't getting accepted?

How many times did I have to reach out to the listing agents for financials because by the time the agents got them, an offer was already accepted.

You could still evict for other reasons.Allowing Tenant B to stay in the unit basically accepted them as a tenant.