It doesn’t seem to be your style, but, I myself would go a bit more tradition middle name: [name_m]Abraham[/name_m] [name_m]Michael[/name_m].
[name_m]Abraham[/name_m] [name_m]Shepherd[/name_m] (sounds hilarious to me since [name_m]Abraham[/name_m] was a shepherd.)
[name_m]Abraham[/name_m] [name_m]Sullivan[/name_m].
[name_m]The[/name_m] suggestions of matching a short nickname like [name_m]Hart[/name_m] to [name_m]Abraham[/name_m] to keep him matching [name_m]Gabriel[/name_m] is good.