The bat swarm fills a 10-foot space. That's four of the PCs, as long as they are retreating together. I'm assuming that Lorien and Phar are standing near each other while Caerth and Quinn are standing next to each other. Aureus is likely slinking around on her on, as usual. I'm thinknig she won't be an apparent target unless she attacks. ( [MENTION=6814006]Thateous[/MENTION], I need a hide check.)
I'm going to say the bat swarm is going to go after Lorien and Phar whiel the rat swarm is going to go after Caerth and Quinn.