You need to assign all the lines to a VDN, have a vector queue to a hunt-group with all the stations in that group. Vector control the huntgroup, now it becomes a split. You can design the split so the stations have to login to receive calls so callers don't ring on a unstaffed phone. You can force multiple calls to the phones if you need them to answer more that one at a time. You also can set the group to ring an available phone and log it out if its not answered and return to the VDN to try another.
Or you can cover the lines to a Terminating-Extension-Group and ring 4 phones at a time then cover-path the Term-Ext-Grp to another group to ring 4 more etc....