How is the house titled? Why doesn't dad sell this house, give all proceeds to the two children AND THEN buy a new house? Check with an attorney regarding that -- one who can see the actual papers.
Another option is to refinance this house, keep it as an investment property which his kids can one day inherit, and buy a different house together, once your attorney has reviewed the decree and concurs that this is allowable.
Frankly, I know few people that are still in the same residence by the time they pass away that they were in when their kids were little. Some downsize into more affordable homes or condos at retirement, or use their equity after retirement to pay for assisted living apartments, or relocate, or become sun birds and have a seasonal home in the sunbelt. A properly drafted decree would have dealt with , not just where this goes AFTER death, but the very likely situaution in which the father would wish to change his residence PRIOR to death. Additionally, such a provision is not very forward thinking, because an elderly person, who dies after living in a care facility for any extended period of time, may have elder care assistance liens placed on their home due to such care
It is unrealistic to presume one will NEVER dispose of the childhood home prior to their death. An attorney should review the language to see if the entirety of the agreement has this provision continuing forever, or whether this provision is part of a pportion that only applies during the children's pre-adult years.