He said for the extent that his camera could go he could see there was a lot of cast iron debri He suggested that I shouldn’t proceed unless the seller of the property can create access to the stack line (clean out in the bathroom wall) or install a clean out outside for external access rather than having to rip out the toilet each time there’s an issue.

However, with the COVID restrictions, we're not sure if we'll be stuck with this tenant or not.How would you guys proceed?

The 1031 will let you use all of the proceeds instead of losing a bunch to taxes. 

I believe that if she were to continue down this path, she would obviously run out of money.At this point, my mom is also willing to have me take over the rental properties and/or use these properties for leverage to increase our wealth so that she does not run out of money and so that I do not have to support her with my own W2 salary in the future; thus, I am wondering what would be the best way to proceed with the least risk? 

In retaliation, the floor tenant has proceeded to bang on the door of the upstairs tenant and poke the ceiling with a broom stick whenever they feel that the noise is excessive.

This payout structure is typically defined in your "waterfall" which is a table detailing how the proceeds at sale are distributed and the waterfall should match the terms of the agreement and/or partnership.

You could also consider the 1031 exchange with the proceeds of the sale.

If not, how would you proceed with tracking down the title holder?

The rates on the HELOC are higher than my current mortgage making the HELOC for a down payment more costly, would interest only payments be the best way to proceed with this?

Provide them with the eviction proceedings/completion, tell them what's going on and that it's a big nuisance for you and the tenant and you would like to get a No-Trespass against them (they realllllly should include these in evictions, you know?)