Your father and elder brother's claim to arms is really a non-issue, since any arms you matriculate will be differenced. If you were the first son, then you'd have to get your father on board, but as it is, they would have to matriculate their arms separately. Before you petition a grant for an ancestor, you can ask your father/brother(s)/uncles/cousins that might be interested in their own cadet matriculations to pitch-in on the costs for the ancestor's grant of arms, since that would be required of all of you.

And you don't need to get your lineage back to Scotland if you have an ancestor with a Scottish name that lived in the original 13 colonies prior to 1783 (as EagleJCS pointed out). That is currently a sufficient tie to Scotland for Lyon to grant him arms.