Actually, I agree that all of those points by
quorkboy are straight from the story. People want to get straight to the fucking. I dig it.
But MC is just now coming out of protective father mode. Do you remember how he exploded when his ex accused him of abusing the girls? That's what he fears is happening when he looks at them with lust.
Becca has been trying to show him that things have changed and he can move out of strictly father-mode and into man-mode, because the girls have for sure moved out of strictly daughter-mode.
Lilith is the type of girl that needs to push and push and push just to see if you'll stay where you are. And MC has. He's not going anywhere. She gets that now and her walls are going to fall very quickly. "Dad isn't going anywhere so it's safe to love him." She sees his reluctance to go along with Becca's plans, and that makes him even safer. He's NOT a perv. He's just in love with her.
Abby has been in love with MC forever. Now that she knows they aren't blood, that's the only excuse she needs to give in to that love. She looks just like her mother, so maybe she can take her mom's place. And MC makes constant comparisons to her mom, in a very positive way. He loves Abby, maybe the same way he loved her mom.
Becca is so smart, so manipulative. She sees what Lilith and Abby want. She knows what she wants. They all want Daddy. She's going to make it happen. And MC can either let them love him as they want, or can step back and be just their father. (Lol yeah, right!)