Hey Richard,
I am not sure that I understood what you are not able to do correctly but here is what I would do to achieve what you mentioned.
1 Create a Repeating group for the first two elements
2 Create another repeating group with only one cell
3 Create another repeating group inside repeating group n2 with the rest of the elements
This should achieve what you want
It should be something like this:
Please let me know if this works
Best
Julian