This is not precisely on point with respect to this thread, but I thought that it might illustrate some of the issues.
Mom owns a C corp.
One member is the Company, and S and Cousin become the other members. Mom might become a member as well, but that is unlikely. The Company gets a frozen interest, with a fixed rate of preferential return and a preference upon sale or liquidation. Son and Cousin have to buy out the Company's interest in the event of Mom's death. Obviously, there is a problem with respect to substantially appreciated assets and the possibility of sale within 10 years.