I'm not convinced they can't be separated. They already left Sou along with Suzuki to chat about their own thing. They also let him meet Yuri along during that initial encounter.
That also doesn't account for non-school encounters where it's just one person.
The biggest way to force it through would be to just have Sou want to approach someone of his own volition. I don't think they've actively prevented Sou from going somewhere he wanted to go yet. And even if they tried, he should be able to sweet-talk them.
I never said they can't be split up. It strongly depends on the situation.
Take the thing with Suzuki for example - he's a guy, so there's way less risk for Sou, despite two guys fighting would become an issue in and of itself, but anyways. The lunch break on the school roof was a situation where the two knew each other already and it was a secluded area with no way for others to pop up out of the blue. Do you remember the scene on the train when Sou and Suzuki first met for real and then clashed. They got separated and one guard of each team stayed with their respective guy - and that was despite them being in a male passenger car which should be rather safe.
The toilet meeting with Yuri happened at a place where usually girls rarely go to anyway, let alone guys. No one would expect it and lay a trap there (from a guards perspective). That also happened on the school grounds, so it's still a relatively safe area for Sou. Not to mention the guards were a bit giddy about meeting Sou's family afterwards. But yeah, usually one of them should have gone with him there.
That's why I never said it was mission impossible for Sou. Still, it won't be easy for him to convince them, but it depends on the situation. I cannot imagine they would let him run around unguarded when they are "out in the wild". That would be going against everything an escort student has to take care about.