Help with First Sub 2 Deal

[Ethan Henning]

Hello, 

I am purchasing my first creative deal and we have negotiated terms for the seller to carry financing on a  short term balloon structure to give us enough time to either flip the property or refi. The seller has an existing loan on the property so we are purchasing the home subject to the existing mortgage. I am looking for information on how to structure the auto payments to ensure the existing mortgage gets paid monthly. My thoughts were to set up a joint bank account with the seller where our interest payments go into the account and the existing mortgage gets auto drafted from that account and I can make sure that its getting paid for the 3 months or so while we a rehabbing the property. Does anyone have experience with structuring this or any insight? I greatly appreciate it!