The property has been owned outright for over 70 years, has had the same tenant over 50 years (a utility company), and we are looking at taking out around 40% LTV, and the mortgage payments would be covered 2-3x by the rental income, so very stable, safe lending situation. 

About 5 years ago we hopped in a RE syndication and pulled out of it recently to take a more active role in our investing (returns where meh), along with trying to supercharge our financial goals in retiring early. 

Properties in good areas, whether SFH or MFH, tend to attract more stable, responsible tenants who maintain the property better.

I built a solid retirement portfolio from SFHs with added value. 

At BiggerPockets, we've actually worked hard to keep our core membership costs stable while significantly increasing the value we provide.

I’m retired.  

My question is how will a house sale affect his retirement and selling me the house at a discount will affect me?

Property is exempt from STR permitting because the jurisdiction considers it to be a commercial lodging establishment.We've been pursuing an SBA 504 loan for it, which was going well until we discovered that the sellers have operated it only part-time the last 12 years -- intentionally blocking 60% of available room-nights because they just weren't up for running it full time in their retirement. 

I don't think I will ever fully retire but I plan to be doing less active work in the future, i.e. not focusing on writing new loans and not flipping.I am lucky that I can easily handle a down turn and be just fine if things soften even for an extended time but I still hope that doesn't happen.

Equity and retirement assets wont do anything for DTI unless youre retirement age, have a plan in place to create income via IRA distributions, and have a sufficient balance for the distributions to continue for at least three years.