Have been in similar situations before, including a sudden 5 front war. Needless to say, my Getic armies were up to the task.

Started another Hayasdan campaign yesterday. Took the Eleutheroi Caucasus holdings. The Arche seemed a bit disappointed that I had just beaten them to Phraaspa. Next turn, declaration of war, and a futile siege of Phraapsa. Fun, as I was the only ally that had not betrayed them; and instead of sending armies to deal with Baktria, Pahlava, and to a lesser extent the Saka, or to the West to deal with the Ptollies and the Pontic upstarts, they send them to me. Turn after that they manage to get a cease fire with the Ptollies. Hope I can hold out.

Strange enough the only two factions that actually never betrayed a peace or an alliance (with me) in game are the Epirotes and Sauromatae.