That's a bit more involved than "Can I hang my wet towels on your staircase bannister?"
As joint owners of the duplexes, the two families make up an Ocean City staple as familiar as a Mallons sticky bun: the duplex condo association.
"We have an operating agreement for two families living on the same lot," said Richard Fischer, 51, a CPA from Pittsburgh, whose family has long spent summers in Ocean City. "Who's going to take care of cutting the grass? Planting flowers? That kind of silliness."
But there was nothing silly about the arrangement the two families had to work out post-Sandy.
Top - with no damage (and no insurance settlement) - agreed to demolish the entire house and rebuild.
Builder Scott Halliday of Halliday Leonard marveled at the arrangement, how nice and genuine both families seemed, and quickly found a model home, one that doubles the upstairs space and expands the downstairs, and an exterior (Sea Glass Green) that both liked.
"I think this is the hard part," said Diane Fischer, 51. "Their house is not damaged. They could have lived in it this summer. Our bottom part: We need electrical. We had mold."
In a summer culture where people fight over parking spaces and scheme to avoid beach tags, this scenario would seem to have at least the potential to unravel a long-standing happy relationship among families that all hail from the Emmaus/Allentown area.
In fact, Ron Rieder, 80, was principal of Emmaus High School when Rich and Diane were students. Carol Rieder, 66, was Diane's French teacher.
The families each bought half the duplex in 2002, splitting the $225,000 total cost. Diane Fischer's parents - old friends of the Rieders' - have a home two doors away. The Rieders were already renting the top half when the owner decided to sell.
Bob Bieler, Diane's father, was the mastermind of this arrangement.
He had subtly and not so subtly encouraged a situation in which his friends live two doors down; he had spread out his children and grandchildren beyond his own home, where they had all crowded in, to another duplex on the street; and he now had a place to store his 39,000 bicycles: Ron Rieder's garage (and Ron's joking estimate).
Their sale agreement called for the Rieders to own the garage, which was damaged but not covered by insurance. Neither, as it turns out, is rebuilding because the downstairs unit was damaged and yours wasn't and you happen to be super nice nice people.
The Fischers did get insurance money but not much: $45,000 plus an Increased Cost of Compliance payout from FEMA of $30,000 to raise the structure to meet new flood elevations.
Would that tight-knit multifamily clan anchored mid-island around the corner from good old Kessel's hamburger joint fracture? Would the good will of the Reiders - Ron, mostly interested in finding a tennis game; Carol, thriving in a summer community she'd found at the 22d Street beach - hold?
In this case, their connections did not unravel at all, but have been pulled even tighter by the storm. Said Rich Fischer, "Ron and Carol told Diane and I whatever you want to do, we're behind you 100 percent."
Carol Rieder, busy picking out appliances and granite and meeting with builder Halliday last Thursday in Ocean City, said the couple basically drew a deep breath and plunged ahead with the extra mortgage (they're still paying off the top half of the phantom duplex). Hey, they'd wanted a new kitchen anyway. The house came down last month.
"We didn't expect to be tearing down the house to get a new kitchen," Carol Rieder said. "But we kept telling them, what do you want to do?"
Roger McLarnon, director of community operations in Ocean City, said the Rieder-Fischer arrangement was unusual. Although many of the 2,000 structures damaged by Sandy in Ocean City were duplexes, the most severely damaged were older structures typically with one owner and a rental unit. The newer units with two owners were built higher.
The Rieders' congeniality belies their strong attachment to the top half. "It was heartbreaking," Carol said. And they lost a summer.
Their top half, though smaller - the families agreed to a 60-40 informal split of the water bill, which lawyers warned them against - had the charm of a sloping roof that gave grandchildren their special play cubby. It had the old-fashioned striped awning. It was so small, though, that the Fischers would have to leave themselves to let the children and grandchildren have a week.
Then there was the promise the Fischers made to the previous owner - from whom they had rented for years - that they would not tear it down. They concluded that was inescapable, the threat of long-term consequences from downstairs mold in their minds.
They still have former owner Bill Etherington's bicycle (stored seat side down so the gears were not ruined) and a few of his belongings they will keep in the new house. They are sorry it turned out this way, in that respect.
But neither the Fischers nor the Rieders wanted to let their all-but-family co-owners down. And so the house was torn down, and the pilings were driven.
In fact, though, both had plan B's the other was not aware of.
The Fischers actually got a last-minute offer to buy into half a duplex closer to the ocean that was undamaged by Sandy.
They agonized, but ultimately decided they couldn't back out on the Rieders, who had been so stupendously accommodating. The house was still standing, but the plans were too far along.
The Rieders, though, had a son, a veterinarian, who would have bought that bottom in a Margate minute, but is happy with the planned roomier top.
It all starts to get a little Gift of the Magi-esque if you think about it too hard. In the end, the glue loosened, but the families remained bound.
They even tried to keep the design of the old duplex that had an inside door that connected both units. But it didn't work out. At least not literally.
"The door that separates us was never locked," Carol Rieder said the other day.
Contact Amy S. Rosenberg at 609-823-0453 or email@example.com. Follow on twitter or instagram @amysrosenberg.