animate motion for a group?

I've grouped an (Smartshape) arrow and box together.  I want them to move left to right as a group, as if the arrow is pushing the box.  When I click on Effects in the Timeline for the group, everthing is greyed out. I can click on the arrow and the box individually and do effects > motion  path > left to right., but I can't coordinate their movements.  Anyone know of a way to do this?

Thanks.