His wives/Harem are standard equipment for him, so they're around the area.
I still don’t see how this automatically means all of Regulus’s wives should be right next to him. They can be anywhere from 0 to over 100 km away, yeah the further they are, the more dangerous it becomes for him ofcourse since he can’t leave their range. But at the same time, the closer they are, the more likely they get caught up in the fire.
It’s not like Obito has some massive AoE explosion that covers thousands of meters, at least, not that I remember. The only time Regulus had all of his wives with him was in Priestella. In the Ex story against Kurgan, he only brought two. In Arc 4, when he fought Petelgeuse and Fortuna, they were nowhere to be seen. Pandora later mentioned that she was gonna send him to where his wives were "in the mansion", so thats where they probably were in some capacity, it’s unclear if he had brought any with him (like outside the woods or something). In Arc 3, when he fought Crusch and Rem, they also weren’t there.
So idk why we assuming all of them are automatically around him, The OP hasn’t specified their exact distance, so if we go by what’s consistent, Regulus usually only brings around two wives to fights, while the rest are elsewhere. The OP needs to clarify where the wives are and how far they are, since he made the matchup.
Obito’s profile states that his range extends from several dozen meters to thousands of kilometers with ranged attacks. I’m not sure which specific attacks justify that, but it wouldn’t matter anyway, if the wives are, say, 10 km away, they aren’t the enemies in this battle, so they wouldn’t be his target in the first place.