Failing to appreciate it is putting it mildly. They'll likely sue over it, in an attempt to set aside the will, claiming their siblings exerted undue influence over their parents. Either that or they'll have to prove their parents lacked mental capacity when they made out their wills. Those are basically the only two grounds under which someone can sue if they're unhappy with their share of the pot.

"It's not easy to determine what was in mom's or dad's mind, or how much they were being unduly influenced. And mom and dad are no longer around to say whether they were unduly influenced," Dribin says. "I have learned over time not to jump to the conclusion that the child who was there and got the lion's share did anything improper. Very often, when you investigate the facts, there was no one else to step in."

Sometimes the parents aren't even sick when one child moves back home, and his siblings fear he or she is siphoning funds out of the estate before the parents are even dead. One financial planner says he knew a woman in her 80s whose son moved back into the house and one of the first things he did was throw out the caretaker, because he saw the expense eroding his mother's estate and thus his inheritance. His siblings caught wind of it, threw the brother out and got the caretaker back.

In some instances, one child has borrowed money from his parents, for, say, a business venture, and the other siblings see that as reducing the size of the estate and thus their inheritance. Some clients take such loans into account when doing their estate plans, but it's the exception and not the rule, estate attorneys say.

John O'Grady, an estate attorney in San Francisco, says in his 25 years of practice, he's probably seen 100 cases in which a child moves back home to take care of the parents, and he still isn't clear whether their intentions are selfless or selfish. They wind up with complete access to the parents, in some instances gaining access to all the money and accounts. The parents may even give them a credit card or other gifts, and the ability to sign checks.
"It happens routinely. And then mom and dad die, and the other siblings find out about all these gifts, and they get really angry, because they feel like the caregiver kid took advantage," O'Grady says.

The two most contentious issues that come up in the estate process are how to handle the family home and the family business. Real estate is problematic because other assets, like stock, can be liquidated, so those wanting cash can simply sell. But when children with vastly different financial situations must decide what to do with a shared piece of property, those income disparities will weigh on that decision. A child earning a substantial income, for instance, might want to keep the parents' beach home in Nantucket, while the child with less money may not be able to afford the taxes and upkeep and will want to sell it. It doesn't help when the real estate is the family home, and the parents have a directive that says, "Whatever you do, don't sell the family home."

"That's probably the worst thing they can suggest," says John Hillis, president of Hillis Financial in San Jose, Calif.
One solution, advisors say, is for the parents to put money into a trust that would cover the taxes and maintenance costs for, say, five years, so the children can assess whether they really want to keep the property.

Of course that presumes no one is living on it. Sometimes, one child will move into the parents' estate and live there rent free. He'll refuse to move out when his siblings want to sell the property, yet he won't have the money to buy them out.

Ryan, the mediator, is working with a family of four children in Texas in just that situation. One of the two sons had an estate on the Gulf of Mexico that was destroyed by a hurricane, so he moved in with his mother-the father had already died-while his own home was being rebuilt. The mother recently died, and his siblings now want to sell the parents' $4 million estate in Houston, but the son refuses to leave. His brother and sisters don't want to throw him out because they're afraid of him, Ryan says.

"There's a lot of alcoholism and sexual abuse in this family. There's a lot of anger and hurt feelings and not being able to confront issues because there's so much fear of the brother's anger," Ryan says. "It's never about money. It's always about some underlying issue that they're upset about. This happens a lot with wealthy families. They see the money as a weapon to be used against each other."