Dice, dice baby.
Usually, events in RPG's are determined by a combination of role-playing and dice rolls. When there's a big gap between player knowledge and character knowledge, rely heavily on dice rolls.
It can be slightly jarring, but players will generally react well, because it's fair and rolling dice is always fun.
In my experience, most meta-gaming is done by experiences players trying to get get advantage.
Assuming you are starting with an immersive play style, you can solve this in character by interpreting the actions of the meta-gamer in character, without breaking the action. Show that the meta-gaming actions make no sense, by the reactions of NPCs, etc. Set the expectation of high-quality play.
Most players, even novices, will quickly see that the only way forward is to play their characters properly. If some newbie just isn't getting it, and is getting frustrated, you can stop the game for a minute and give a short lecture.
Other tips for you situation:
If meta-gaming persists, issue a warning.
Limit any exploitable details you give to the separated parties to just what's needed.
Get the party back together as quickly as is reasonable.
An illustration - After your tavern goers lose their fight:
Larry: 7 damage? I'm at zero hit points.
GM: You're down. The good news is they don't kill you. They bind your wounds, and your hands and feet, put a sack over your head, and trundle you off.
Larry: Can I tell at all where they are taking me? To a basement, or out of town?
GM: Your character knows, but the others don't. I'll tell you when it matters. You're losing consciousness.
Moe: You know, I think we should probaby check on the others.
Curly: How would we know to do that?
GM: Curly, Moe starts talking crazy. You are afraid you might have to restrain him.
Moe: I check the roads out of town.
GM: Moe, you hear a demon's voice in your head telling you do do things. You shut your mind to it, knowing that to listen to its urgings would bring only madness, despair, and a permanent loss of hit points. You do get a good price on that healing potion you wanted, 5GP off!
GM: A boy runs up to you, "Hey you guys, your friends just got kidnapped!"
And this is where the skill check rolls come in to try to identify and find the culprits. If nobody can get a decent roll, then the next morning a ransom is waiting for the remaining characters (or something).