I am a Veteran and trying to assume the loan from my sister in law who is also a Veteran.

You should follow the law and best practices of long-term rentals, not short-term rentals.2.

I did hear about the structural issues a few times but didn’t realize it was that much.

If you dont already know the laws for STRs in Philadelphia I would caution you to not buy this deal and start to learn what is needed first, then find the deal.  

I have a lead on a nicely performing and off-market SFH near the SIU School of Law and would like to make a move if possible.

The way I see this is :1. not utilizing the calculator well enough (eg. undervaluing my rent estimation) 2. there is no good properties in the area to invest. 3. other issues that I may not see (blind spot). 

My issue is my credit took a hit during renovations and I had to evict someone that wasn't supposed to move in a property.

But with zero enforcement since they don't issue or require STR permits.  

While insurance has covered some costs, the process has been stressful, even with a property manager (their responsiveness to these issues has been slow).

No issues with zoning?