OP I hope your exam has gone well today and wish you all the luck in the world for your future.
Please ignore the few poster's nasty comments. I do not think of you in that way at all.
I think you are listening to your unease and discomfort and questioning 'Why?' and that makes you a good mother not a bad one. I myself am very grateful you came here to ask for advice because it does mean you are looking out for your daughters.
I did not mean to frighten you with my earlier post but the similarities in behaviour of your DP and my SF are chilling. I am also not saying that he is definitely a paedophile but the fact that my own experience mirrors that of other posters here is valuable information that I am now glad I, and other posters, have shared with you and possibly the wider MN community. Someone else may be reading this and think 'Hang on..' If it helps even one person see possible reasons for things that have been niggling at them then I am glad I had the courage to post.
A few other things I am going to flag up. Trigger Warning again
An interest in your DD's dirty laundry both clothes and bedding.
Reactions when the girls have friends round. Intrusive pushing in to be involved or very grumpy moodiness (possibly due to them having support/someone to confide in).
Eagerness to take one or both all over the place. Damage can be done with words. 'Your Mum is cross with you.' 'Your sister is fed up with you.' 'Your friend is no good for you. I'll be your friend.'
Buying things, especially Wow! things, no matter how small. If it's something they really want it's something that can be held over them. I see you mentioned the favourite pop star tickets for Christmas, who is taking them to that? 'I bought you this! Why aren't you nice to me? Come sit with me and we'll talk.'
Overbearing comments on prettiness, loveliness, growing up. Mentions of future boyfriends. 'When you're a big girl and have a boyfriend..' can become 'You're nearly a big girl now..'
Check the cam on your DD's laptop. Does he have a laptop up there with him? Who does your DD communicate with on the laptop? It's not unheard of for friends/boyfriends online turning out to be predators known to the family. After all they have insider information on how to more easily get closer to their target.
Stopping there as getting a bit angry now but I wish you all the best OP and I hope you feel able to come back here. I know there is some difficult reading but part of the problem with CSA is that most people turn away from discussing the methods, how the child feels at the time, and the results of how these monsters get access to their victims and their families. If these words help even just one child then it is worth writing them.