When Arun Paul’s parents were in their 70s, he began searching for a duplex in his neighborhood in the Bay Area where they could live. The plan was that Mr. Paul would be close by, but his parents would also share the duplex with their friends, another older couple.

It was important to Mr. Paul that his parents, who emigrated from India in the 1960s, would have other Indian people to be around, especially as they aged. “Growing up, I could always feel that there was something they left behind, like a really important piece of who they were,” said Mr. Paul, 49.