It's pretty much just RNG, the Mom/Sis have a chance to wake up after each time you try something. If you haven't used Mind control on them on that day, then you can use it tell them to go back to sleep and forget. However, that just acts as a free save from being caught, they can just wake up again.
I dunno, if it's related to the total control over you have over the person, but regardless if it related or not, you can boost your control by complimenting the person in question. For example, saying the mom is beautiful, the sis is hot, etc. You can say it twice, and each time raises control by 2%. No idea what the correct phrase to raise control is on Clara and Monique, but be aware saying vulgar things makes you control drop pretty heavily.