MR is adamant that cops would not/could not find anything incriminating in his car. If his car was supposed to be with CP, and MR is at home asleep, how could MR be so positively sure that his car would be "clean"? If you put that together with MR's insistence that "we" didn't do anything wrong, I think this further indicates that. . .whatever they did, they did it together.
I am also with PalmyraDad's thinking that whenever Kortne was moved from the location, she was moved in her own car. This is also how/why MR is so confident that LE couldn't find anything in his car.
I don't think anyone has ever accused MR of forcing himself on women, but he has expressed open anger about women turning him down. As for CP, I speculate that there may be many "rumors" that he has a consistent history of becoming violent toward women, though only when he is intoxicated.
I believe these two are "sticking together" because they both played a part and are using that as a "threat" against the other, if one were to rat. In other words, I suspect they tell each other, "If you tell them I did this, I will tell them you did that." This keeps them both quiet.
Both men are very familiar with the law and both have a lot of "experience" dealing with LE. They, for instance, are well aware that LE needs a search warrant to enter a house, so it's perfectly reasonable to expect they held their breath and waited for LE to leave. But as a side note, I believe CP is the dumber one and the "weaker link". If anyone is going to crack, he will be the one to crack first.