You're both friends
BUT I CAN COUNTER.
Since we are not, unfortunately, engaging a conventional enemy, we will have to employ some less-than-conventional tactics. Order all ships to set a collision course for the lead ship in a V formation, and have the legionary charge its main cannon. Time their speed to put them at least 500 meters from the kresh ships when their cannons are fully charged. Order the fighters to engage the other ships, and since the kresh do not utilise fighters (or at least we have not observed them using small craft), we can arm them for anti-ship combat and have them engage the other ships at point-blank range, possibly destroying some. As soon as the fleet is in position order the legionary to fire its main cannon, and have the other ships fire their laser cannons at point blank range! Then break off the attack and select a new target. Have the fighters finish it off if it isn't already dead.
Rinse wash repeat, and alternate which ship is using the main cannon and have the ones which are drained from the cannon use to engage with torcreepes