Miniatures wise, you would need two dwarf heroes to lead the two dwarf warbands you have and a Dale hero to lead the men. (A warband is 1-12 warriors led by one hero). The hero needs to come from the same army list as the warriors, so for your dwarfs the rangers come from the Durin's Folk list and the Grim Hammers come from the Erebor list while the men come from the Dale list.
Unfortunatly, I think the stats for these figures are split between three different books (LOTR: The Free People (OOP), The Hobbit: An Unexpected Journey, and The Hobbit: The Desolation of Smaug). An Unexpected Journey is also the latest rulebook, so you probably want that anyway.