[quote name='Blackout']I have Shepard (soldier), Ashley, and Garrus as my party.[/QUOTE]
Hmm... unless you're just looking to romance Ashley, she's pretty redundant. Can Garrus even train in shotgun? He's a beast as a sniper, but I'm pretty sure he trains in assault rifle for close combat, give him a good AR and he should hold up a little better. Honestly, I'd probably go full AR's for that team, or two AR's and one shotgun.
If you really want to keep up the Combat abilities, I'd switch her out for Wrex and gain a shotgun-juggernaut with biotics. If you insist in keeping the same team (still capable), using the power wheel to issue commands (and pause the action) is your best option.
Place your teamates midway through the corridor, and have them hold position, that'll provide you with extra cover. As soon as the action starts, turn on your soldiers invulnerability powers; after the power activates, immediately power wheel again and use your weapon's Overkill feature. Ashley may survive, Garrus is almost guaranteed to die. If you can't kill them all, run like hell to the main entrance.