Did he molest his step daughter?

I don't think so. I think he was genuinely rehabilitated.

I think he did, or at least was thinking about it, the way he thought about it for a while before doing it with Una. And I think Una realized it too, in the final scene at the end of the driveway, when he denied it and said she, Una, was the only one. That's why she walked away in disgust. She knew he was lying, the way peadophiles always do.

It's left quite deliberately ambiguous and for the audience decide its own conclusion.

I think he did, just the way he talks to Una at the end and she walks away not cause he's molesting the step daughter but that she's realises she's not his number 1 anymore. That's the scary thing imo about it. She's more jealous then disgusted.