A friend transferred ownership of her home to her two sons approximately 3 years prior to her death. A third son, having 2 adult children, passed away more than 15 years ago and prior to the transfer. Do the deceased son's children have any legal claim to the money from the sale of this property?

Nope. There is no requirement that a parent must make equal value gifts to each of her children, or her grand children.

Well, that really depends on how the will and transfer was done. If she directly transferred it to her two sons (not upon death but while still alive they took ownership) then no. However, when it comes to wills there are very sticky wording issues that can be challenged in court. (which is why it's best to have a lawyer draw it up for you and make sure all bases are covered).