Not a wise decision. Although your family owe the Bruces a great deal, you must think of the current situation. David is still too young and Edward Balliol already has many supporters. Capitalise on the situation at hand. Back Balliol!
Strike a deal with Edward Balliol. If he promises to acknowledge your authority over lands in the west, you will pledge military support to help him defend against his enemies.
Attempt a reconciliation between your family and the MacDougalls. Try and convince them that a united Gaelic community should be the mission of both families, not siding with Balliol.
Play a card