Ianto is not in the mood for these shenanagins and will likely swim to safety and pout. He'd be down for Defense Force rescue coordination but no actual rescuing. Bring him some binoculars or something and he'll watch for stragglers and be soggy.
Phanan if terrible things happen to Chuck (WHICH THEY SHOULD OH MY GOD) shit will be lost. Otherwise he will probably get a floatie shaped like a duck and play with that and maybe rescue people or splash them.
Kanji will be on rescue duty. Pros - big, strong, great swimmer. Cons - will be wearing his swimsuit. Are you prepared to be manhandled by someone in that?
Aigis will probably head to the pet cafe and start talking to the dogs about safety issues. She will also be swimming, jumping and roboting around rescuing people. Very competent, good swimmer, able to break through buildings or barriers to people who are trapped.