Homer and Marge go... somewhere and leave Grampa in charge of the kids. Bart and Lisa misbehave. Grampa guilts them into cleaning up by pretending to cry.
That's right, you heard me!
Pretending to cry!
I can turn it on and off like a faucet.
It's a couples retreat because Marge doesn't feel Homer gives her the attention/respect she deserves, so this retreat is time alone (together) with other couples to improve their communication.
Homer however just wants to go fishing, which isn't the purpose of the retreat (and further ignores Marge).