Lisa, Anna is correct...this will work just like any other "typical" transaction.
Several questions come to mind. First, are you in a home now and your parents are buying your ex-husband's interest out of the home? Are you divorced or seperated? You don't need to answer those questions here, however, the answers to those questions will drive the type of advice you need.
if you are looking to buy a new/resale home other than the one you lived in with your husband and you are divorced, then there are other questions that need to be answered. Will your parents be buying the house and retaining ownership allowing you and the kids to live there? Are you buying the home and your parents are assisting with the down payment? Again, depending on how you answer those questions will determine the best course of action to take. There may be tax or legal questions that arise as well depending on how you want to structure the transaction. In that case, you will want to bring in a CPA and attorney for those answers. You need a realtor to help guide you through the home buying/financing process that can work with you and other professional advisors (CPA, attorney) to make sure you are getting the best advice possible for your particular situation.
Unfortunatley, there is no "easy" answer becuase there are many issues and questions that need to be addressed regarding your particular situation. The bottom line is that a realtor with many years experience with a proven record of honesty and integrity can help guide you with the proper advice.
If you need referrals or would like to ask other real estate related questions, it would be my pleasure address those for you. Best wishes for a successful purchase.