And your quote suggests it’s their fault that Regina is scheming with Cora instead of it being Regina’s choice to scheme with Cora.
So, you feel that Regina went back to scheming because the Charmings handled the situation wrong?
Or do you feel she went back to Cora because it was her choice to do so?
And the answer can’t be both. You can’t blame someone else for a choice you make. It might have had influence, but it’s not the reason.