I don't know either, but there should be, back when Sios used to troll me and get me to add him to my town, then add residents with names like oooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooOOOOOOOOOOoOOOOlsdifjeIjffjdjsjsfvndjfgnfn blah blah blah lol it was annoying to the point where I would pay users to remove them lol...

I second this suggestion to adding a ability with such results.

 

I don't think its possible. You can do more than 1 member at a time within the same command (/rg removemember townname bob Mary frank bill), although you will still have to type them all out.

I always pull up the live map and click on my town to show all the members. Just have your minecraft and live map next to each other on your screen and start typing all the names out.