A foul smell upon entering the building ( something from carpet I assume) has several spots of leaks on the roof (almost every bedroom has one).

You should also figure out any hard to eliminate odors that may be present 

The neighbors next 2 doors grow weeds inside and use them on their porch creating strong odors, etc.".

Don’t use artificial air fresheners to cover up odors; buyers often suspect you’re hiding something.

Might be something turning them off like an odor or bad layout.

Change mine to the gumpy super tall centers that do nothing but draw fouls 

The scope of work includes electrical and plumbing upgrades, gutter replacement, water infiltration mitigation, interior and exterior painting, odor removal (due to animals), wall repairs, full renovation of bathrooms and kitchens, and structural reinforcement.We estimate the total rehab cost to be approximately $200,000.

Unlike carpet, LVP does not trap odors, allergens, or moisture, and it is easier to maintain. 

Any positive experiences with removal of odors from tenants using bio sweep?

We do not suspect foul play because the tenant's relatives have reported to the remaining tenants that the MIA tenant has moved in with another relative (but did not give that MIA tenant's new contact information).