How do we put the money in the right places to make this happen?

[Ed Lopez]

Hello, I am looking for some advice on how to handle financing of a new primary residence. Here is the situation. I am looking at joining forces with my mother and buying a 10 acre property with two separate houses on it. The property have two separate addresses but but cannot be divided currently. My mother owns her current home outright which is valued around $280-300K. I have a mortgage on my current home and owe approximately $280K on a home valued around $370K. I would like to keep my current residence as a rental. My mother is leaning towards selling her residence but is open to the possibility of renting. The new home we found is an off market deal and the seller is looking at getting out as quickly as possible because he is moving out of state. We came to an agreement on a price of $625K for the new property and the seller would like to start a 30-45 day escrow asap. We would like to leverage the equity of my mothers home for a down payment on the new property and some extra money to do some remodeling. We are trying to decide weather taking out a conventional mortgage on it or doing a HELOC would be better given the time constraints.

I'm going to throw on more crazy wrench in the plan.  My mother is married but does not live with or share any finances at all with her husband.  We both want to be sure that he has no stake whatsoever in the new property if they happen to part ways down the road.  

Any advice is appreciated.  I can supply more info as needed but that is the basis of my current situation.  Thanks.