With interest rates low, sales prices down in many markets, and First Time Homebuyers getting $8,000 credtis...land contracts are becoming rare. Most sellers will require a large down payment to feel secure with the risk. I suggest 10% or more for my clients. If the property is listed with a Real Estate Brokerage it is likely that the Seller will require that the commisions are paid by the Buyer as well, and for good reason. The seller is taking the risk that the banks won't. They are letting someone move in to their home, not getting the equity they may have been looking to get through a traditional sale, and still holding title and possibly the mortgage on the property until the land contract is satisfied. It's a large risk to take that carries a lot of liability. Land contracts were popular in the early 80's when interest rates were high but not in today's market.
If your daughter's family has the means to place a large amount of money down then you may be able to find someone who would entertain such as offer. If not my advise would be to continue working on improving credit scores and putting money aside for Earnest Money, Down Payment, Closing Costs and Prepaids.
Talk with Loan Officers now to get an idea of what areas of their credit would be best to focus on in order to become pre-qualified. Ask them if they could refer you to a good credit counsler.
The road to homeownership can be hard, but the pay-off is well worth it.
I wish you the best in your real estate goals and hope you find my advise to be helpful, even if it's not what you may want to hear I hope you find that the advise is honest and with good intentions.