Now i understand what's the issue here bud,the quest that followed up made people believe that nuns wants to have sex with priest at all cost,like you explained they didn't had sex with him ,yes that's right but it's not like at any point they didn't wanted or wouldn't have done it.
The reason they didn't slept with priest is because he couldn't get his pp erect and not because they didn't wanted to sleep with priest,moreover when priest couldn't get his pp up,nuns rushed and asked help from hunter so that priest can get his pp up and they can have sex.
Issues is not whether they had sex or not but it is that they would had no problem in having that,like you explained that they have reason to go such length to do some kind of experiment or something,that thing doesn't make them whores or slut even if they had sex with priest,but just wierdo and as person you wouldn't want to have relation of any sort with those type of girls who can bed with anyone esily.
Them not fucking was good part for NTR haters,but i guess the reason given is not to many people liking,nuns aren't whores or sluts, but also someone you can't trust or don't want to have as your lover,since they would fuck with anyone if needed for their purpose.
All in all having like these nuns is not disastrous move,but why defend this much? You don't need to bud, it's okay it's your story to show however way you want,just don't say that these nuns are main lis or something that will break my heart,if they are side character then it's okay it doesn't matter much if they actually would have been sluts.