I would probably make an invisible entity in between them, assign that the mouse move action, then make the spheres' action just a loop that keeps them into the same place relative to the mouse_move entity.
Code:
// !untested!
var invisible_ent;
// assign this to another entity -- doesn't matter what, you won't see it
action move_me_by_mouse
{
my.invisible = on;
my.passable = on;
invisible_ent = me;
// your mouse move code
}
action sphere
{
while(invisible_ent == NULL)
{ wait(1); }
you = invisible_ent;
vec_set(my.skill50, my.x);
vec_sub(my.skill50, your.x);
while(1)
{
vec_set(my.x, your.x);
vec_add(my.x, my.skill50);
wait(1);
}
}
EDIT: I don't think you can assign an action to a group in WED, only individual entities.