Yes, but lets put these in context. One of those daughters has been wanting to be Frank's lover since she was a young teenager, the other has severe daddy issues that she mistook for anger and realized was actually love, the girl that her daughter played with also had a crush on him from a young age and her parents are pushing her into a relationship. With these girls, Frank has never had a sexual thought of them until Becca launched her plan.
When it comes to Beth, she isn't a stranger. She and Nessa spent a good amount of time with Frank when he was their realtor. Long enough for Beth feel the need to scratch that itch that Nessa can't scratch, and for him to be relaxed enough around her to consider doing anything. As for Darla, she was willing, he was able. Same with Madison. He only hesitated with her because he was worried about Becca and Lilly's reaction since they were now together.
In fact, Beth, Darla and Madison kinda disprove the "Frank is weak" narrative that people like to cling to. He got a green light with a married lesbian (who was actually bi) and took it, got a green light with Darla and took it, and got a green light with Madison and took it. The only girls he has inner conflict over are with girls he considered nothing but daughters.