War of the Wild West by Scott Tomasheski

The temporal war between the Council of Time Defense and the alien warlord Klomtoo has reached a new and deadly battlefield on the American western frontier, circa 1866. Now, as their younger selves face the overwhelming might of an armada of time-traveling warships, August and Mrs. A must undertake a perilous journey, beset by dangers at every turn, to find the one piece of technology that might avert a Timeline disaster!