How do you get all four player to "fight"?

I have two towns. In my main town, on an android device, I can send as many as four folks to fight a single monster. Since the payout is 4*150, I always do that. I have monsters all over that town. In my other town, on an iPad, i can only send one fighter at a time, so right now it only has two monsters available.

http://i.imgur.com/gUmHw4z.png

http://i.imgur.com/lxlmAcg.png