Hmm. Mother-daughter, huh? I figure a lot of people are going to think Lester's going to get them both in a threesome, so I'll toss out different prediction - well, similar predictions A and B:
A) Lester follows Sarah/Mom to their destination, manages to get Sarah alone in the room, fucks her like usual, Mom comes back to the room and secretly watches them, gets turned on watching Sarah being Sarah, and now Mom's engaged in the story with Lester.
B) Lester follows Sarah/Mom to their destination, manages to get Sarah alone in the room, fucks her like usual, Mom comes back to the room and secretly watches them, gets disgusted watching Sarah being Sarah, goes home to 'console' Dan, and now Mom's engaged in the story with her son-in-law.
Boom!