If a person in foreclosure agrees to a sub2. what forms are required
You will need written permission from the sellers to check loan balance and amount needed to cure the default including the late payments, late charges, attorney fees, and other fees like appraisal and inspections made by the lender.
You can use an earnest money agreement or just get the deed if they have no equity. If they are financing some of the equity you will need a note and deed of trust if a deed of trust state.
If you want to set up a trust to own the property you will need the trust agreement papers as well.