Recently I heard from Sarah, an old friend, about a hard situation she's in that I'm sure many Caring.com readers can relate to. Sarah's mother-in-law moved in with her and her family more than a year ago, and since then Sarah's had a really hard time dealing with her husband's siblings, who aren't helping out as much as they promised.

But what Sarah's finding even more stressful is that the expense -- both in direct costs and in time lost from work -- of having an elderly person join the household is much greater than she expected. And what really galls her? No one else in the family seems motivated to chip in. "This summer it really got to me," Sarah told me. "We were stuck here in the Midwest heat, working ourselves to the bone keeping up with our jobs and caring for mom, while my husband's sister's family went to the Bahamas, and his brother and his wife spent weeks at their lake cabin. They didn't invite their mom to join them, and it never occurred to them that we could use a vacation too."

The problem is, it's much harder to get situations like this straightened out after the fact, after expectations have gelled and things have settled into a routine. So here are some suggestions culled from elder planning experts for how to set up a working financial arrangement with siblings before your parent or other family member makes the move.