It seems to depend on several factors, age, type (single, double, manufactured), and location.

The articles you are reading on google normally skip a lot of important factors to get to the benefits of a Series LLC. 

If they come in as partners, they can deduct the interest expenses directly against their share of income from partnership.If they come in as lender, they can still deduct the interest as investment interest but might be limited depending on various other factors such as need to itemizing deductions rather than standard deduction. 

Another wrinkle is that I was debating whether it'd be a good idea to get a HELOC on our house as another source of capital, but would that also be factored into my DTI?

Are they doing everything they can to expose properties to the widest possible market?

It’s never been a factor to me. 

There are a lot of factors to consider, but it's generally worth it.

I am asking for advice on how to handle the process of clearing out her belongings in a way that does not expose me to any legal risk and also allows me to begin renovating and improving the unit as soon as possible to decrease the vacancy loss as much as possible while still being ethical and compassionate to her family.On a side note, the other tenant is a building inspector that deals with code violations for the city...sooooooo, I'm going to be pulling permits for everything related to the renovation and hope to create a positive relationship with him while he lives in the unit.Thank you in advance for your advice.  

Opportunity cost is definitely something to factor in as well.

Also, make sure to factor in the implications of future inflation on your assets.