If I've read it correctly, you just want to duplicate a unit and its series of waypoints another seven times? I only ask 'cause the answer is dead obvious when you know it . . .
If so, in the editor, just draw a box round the unit and its WPs (they should go bold), Ctrl-C to copy them then Ctrl-V to paste. If you need to reposition them, do it before you deselect them.
The unit names will increment automatically _1, _2 etc. so you just have to go back through and amend them and any other unit info you need to be unique.
Alternatively, you could try setting a gamelogic as the 'sub'-group and give it WPs with a condition at the beginning. When you want to split your original group, Join the new group to the GL, pause maybe, delete the GL then clear the condition to activate the next WP that the new sub-group should now follow. All very hypothetical . . .