"The only time I ever had to wrestle her was on singing the song. She didn't want to do it," he said. "(She said,) 'No, then they'll say Bette Midler is singing a song.' And I say, 'No, we won't sing great. We'll sing good, but we'll sing like parents, and we'll sing together.'"
Their rendition of the Monotones' 1958 doo-wop classic "The Book of Love" is among the film's highlights.
"They kind of talked me into it, and I'm glad that we did it. It worked out," said Midler, 67. "It's wonderful music and maybe people will go look up the Monotones and see how fabulous they are."
Crystal, also a producer of the film, said he uses movies and performing as a means of working through significant chapters of his life. The film "City Slickers" was about him turning 40. His one-man show, "700 Sundays," is about losing his parents.
"And then this one is about grandparenting," he said. "I shudder to think what the next one's about."
(Actually, he already knows: He's working on a yet-untitled book of essays — "a man's approach to aging" — due out in October.)
Midler, who described herself as "just a player for hire" on "Parental Guidance," said she admires Crystal's sensibilities, and it was fun to finally work with her friend.
"I like to see people at their peak, people doing their best work and really working hard and bringing things to fruition. It's just fantastic," she said. "It's a hopeful picture, and I like that about him. I like the fact that he has that mentality. So to watch him in action is really a lot of fun."
AP Entertainment Writer Sandy Cohen is on Twitter: www.twitter.com/APSandy .