It just eats up a good portion of the lot area, which could potentially be used for another unit or a much nicer outdoor area. 

If you want to look at total expenses over the years, you need to look at total income received as well with your potential sale price. 

But I'm not an attorney, so maybe I'm totally wrong on this hunch.My 2nd comment is directly within my practice area though.

We get traffic studies done to confirm that the roads can handle the potential traffic.

Looking at 50% LTV currently.If your borrowing is TRULY at 50% LTV, a little creativity on your part should uncover potential lenders.  

Find Brandon's videos on YouTube for the "four square" method of analyzing homes and practice.

Very creative, but solid.This also may offer the potential for you to keep your other home and rent it out as an asset, but that's between you and the investor who buys your aunts home to subsequently rent it back to you. 

Investments are investments- I think everyone understands that there is no guarantee for the return, but many potential benefits including the payout coming tax-free.

What methods would you suggest to screen potential tenants? 

The people who reply to texts are different from the ones who pick up for cold calls, so you could potentially be the only one speaking to the sellers on your list.Best of luck!