Panel 1: As they look around the house Nigel tells Phil and Georgia that he built the place himself in 1973 (originally, it was 1953 but leaving that unchanged would have made him ninety or something so Katie changed it) and that there wasn't a neighbour for blocks around back then.
Panel 2: He then goes on to say that he and Agnes raised two girls and a boy who are off and married now with kids of their own. As he does so, Agnes and his mother walk into the room.
Panel 3: Nigel explains to her that no, these are not the people from the church. The two people in front are, in fact, thinking of moving into the house.
Panel 4: Since Mother is on in years and of dubious lucidity, she astonishes everyone by pointing out that there isn't going to be room enough for them all.
Summary: Again, what is the joke? Is it funny that there are little old ladies who slide into irretrievable dementia? Would Lynn laugh now that it's a concern to her?