No, you can have sex with all them in both paths, the difference is that in the Church path one of the girls has to be virgin to complete the ritual succefully, but after the ritual is completed you can go back and fuck the shit out of all of them.
I usually leave Bridget as virgin, because if you advance in Heather story you can find out who is responsible from the murder (spoiler not so spoiler: Heather killed Bernard) and have an extra dialogue option with the abbot. After the ritual I focus on Bridget story until I get her pregnant.
Also, you can't corrupt Heather and Bridget in the Church path, but you can have anal and BJs from both of them without that.