Personally, once they are evicted and I have possession of the property, I would store the stuff for 30 days then deem it abandoned.

Once you have possession back of the property and the lease breakers are gone, try to get the place rerented.

But you wouldn't likely have to give any prepaid rent back until the unit was emptied of all tenant possessions and the unit was re-rented.

Ideally I would like to go ahead and get it under contract and sell it to an investor with a provision in the contract that the owner maintains possession of the property until a specific date.

FHA loans are finicky in that you are only ever allowed to possess one at a time.

I have a home inspection next week and it will probably be OK and I'll take possession in mid February.  

Is the house closed and now in the new owners possession?

You may also want a clause in your purchase agreement that the evictions need to be completed and tenants removed prior to you taking possession.

Control and RollWith the owner being elderly - it would be best to discuss your proposal with their personal representative or relative - shouldn't negotiate with elderly seller - you don't want anyone to think you are taking unfair advantage -Your offer should be that you will offer to purchase the property subject to an assignment to third party - you will need right of possession - a long study period.

That being said it is a little chicken sh*t of the current owners not move their renter before you take possession making you be the bad guy for keeping security deposit especially since she is going back into one of their properties.