What kind of NTR.
Both cases can be given, my stories already have in general created links, so the MC can get to break, now, it is more of sharing and vouyerismo, since the own society of the VN is lustful, it is complex in that sense, there is much psychological factor.
But the MC can interfere, I mean intervene, and in fact some may do NTR, it is possible that he can reverse the situation, other situations is more of sharing, or more of even if the MC does not want to escalate and make deals.
With the immediate family group is where the CM can manage the situation a bit more, since they are not involved in TESS, but the mother was there for a while, so here, depending on the CM's decision, it can be a bit “less NTR, more Harem”, it can also be more ambiguous to corrupt or to share, or to lose control.
The other characters, most of them, if they are corrupted so the options start from “take them out of TESS or to the church, or be part of ‘Harem’; or as the previous ones, but if they have already had and have relations with the cult.