Isn't that what's called arbitrage betting? I've never done it but I feel like it's a legit way of minimizing potential losses.
What you've said is more or less how I see the situation.

Let's say this is a group, as long as they all go through KYC that proves each account is owned by a different person and they simply communicate to place bets together, that's being smart, not cheating.

As for accusations, I usually try to check how the casino responds to the problem. Usually the casino tries to take user's money and delay things for as long as possible, which is like taking revenge on the player. That's completely unprofessional behavior presented by the casino.