Are you working with a Realtor? If yes, then your Realtor should be advising you on this....and going through the Items on the form and explaining things to you.
If not, then use: "Agreement to Occupy after Close of Escrow". This is Beyond ALL the other normal Purchase Offer Paperwork you would need to complete too.
Make sure there is a large enough deposit in Escrow by the Sellers, to be returned to Sellers AFTER you do your Final Walk-through, after they vacate the Property. This will protect YOUR Interest incase there is any damage at the property that needs fixing......not saying the Sellers will do anything...but this is standard procedure I would advise my client to do, to protect them.
If you are Not working with a Realtor, do give me a Call, I will help you through and beyond the transaction!
All the Best,