What I have heard so far is that I could insulate in between the floor joists and use a thicker underlayment underneath laminate flooring in order to achieve noise reduction from above.

I didn't have a renter so I had holding cost, utilities and mortgage until the second week of September 2022 when I finally found a renter. with in six months of ownership the roof started to lose shingles and was leaking, had a roofer to check out the damage and found wood rot underneath. fought with the insurance company to see if they would replace it with a new roof they said no after sending their own inspector and said that the roof was already too old.

Modern vinyl plank with noise and moisture dampening wrapper underneath.

Usually the State has clear guidelines on this and you don't want to be held responsible in the event of soil contamination or environmental hazards to the property or the property owner could come back afterwards on this issue.

I should also note that she lives underneath me in my triplex and is a relatively new tenant.

You are talking 2 separate things here , The tank holds material to allow it to break down , then to go to the drain fields to go into the soil .

There are other costs provided in that publication as well, including compacting soil.

There are plenty of deals like that out here in CA even where the average resale is $700k+ due to soil issues, foundation costs, permitting and utility fees, etc.

Here we have "villas" or "townhouses" which have common walls with the neighbors, but you own the property underneath. 

It's hard to say anything without knowing more specifics - type of foundation, problems, soil type, local regulations, etc.