Not sure you need to record anything if the seller is honest you are OK. Nothing you record will stop the foreclosure. You may record a memorandum of agreement or Memorandum of Contract or some such notice that you have an option to purchase the property. What is the affidavit for ?
Why remove the tenant if they are paying rent ? The owner will have to get tenant to move. You guys have no rights of possession under the option agreement. If you want the tenant out you may get the owner to offer to return the deposit if they are out in 7 days or so. If they are still under a lease that has not expired and the rent is paid that have the right to stay and the owner will have to wait until the lease expires and give then written notice that the lease will be terminated at the end of the lease and they will have to vacate.
Ask owner to allow you to show the property. Tell prospective buyers not to discuss the purchase except in private with you.
unless the tenant is not under a lease agreement she has rights. her rights are spelled out in the original lease. the lease follows the property and new owners will have to honor the lease as it stands, unless there was a provision in the lease that stated otherwise.