Because it is now an investment property it qualifies for sec 1031 treatment. 

Is it common for tenants to stay in the unit if the extermination process is three weeks - three separate treatments?

Basically double, which was the goal.5% of the units will get this treatment.

In the HUD LBP addendum, there's an inspection contingency that reads:The Purchaser has a contingency period that expires fifteen (15) calendar days from the date the contract is accepted by HUD to conduct at the Purchaser's expense, an independent lead-based paint inspection visual assessment for deteriorated paint or risk assessment. 

Our agent did her agent visual inspection when we did the foundation inspection, which was two weeks after we signed the contract.

I am considering doing a DIY treatment right at the beginning of the project so if i missed something, it would take care of it when i put it up for sale.

Was this an investment or an opportunity to help your father.And John is right, there are other ways to establish it as investment tax treatment wise. 

But I am mostly a visual learner/audio learner at most.

Note: this year there was a change in regards to evidence of termites and treatment so if at all possible you will want get proof of treatment from the current owner and give it to the inspector before the inspection.

Also the treatments on passive loss limitations can differ to dependent on material involvement