Seller in second position (Urgent)

[Benjamin Manibog]

I have an investor that just signed a purchase agreement with a seller. The investor agreed to put 300 down and the seller carry a loan for the remainder. After the purchase agreement was already signed, the investor requested an amendment because he needs to get a loan for the down payment. This means that his lender for this loan would be in 1st position and the seller would then be in second position (am I correct?). 

The seller hasn't agreed to this yet, but I wanted to ensure that I was correct. Likewise, if the investor stopped paying the lender (and defaults on the loan) but kept paying the seller that's carrying the loan, what happens to the property? Does the seller gain the property back or does the lender in 1st position? 

Thank you for your time with this.