[Tomgs]

You break fleet formation by going into the Orders menu. The clear group assignment removes the selected ship from the formation and the clear all group assignments removes all ships from the formation.

The only ways to enter into a combat with more than one ship at a time is if either you already have all the ships in the sector with the enemy (like over an enemy planet that just built a ship) or you can hold down the shift button while selecting multiple ships and fleets and then click the move button to move them into combat. Note to do this you must have enough movement remaining for each ship to reach the combat location in one move otherwise if this is a multiturn move the second and later turns the ships and/or fleets will move seperately.