How can I take over their mortgage.

[Tyler Fisher]

I have an off market deal that is being offered 20k under market value. A house was gifted to the sellers and they don’t want to put their old house on the market. They have a conventional loan at 2.9 with a 650.00 mortgage payment. Is there anyway to take that over and just pay the equity they have with a second mortgage or private money loan? Or best way to go about this to purchase this property. 
Current loan is at 95k And they want 150k, comps are 170-180k. 

TIA