Matrix Column Grouping

I have a matrix where the first few columns are not grouped.

However, the final set of columns are grouped on Job Role. This can be 1, 2, 3 or 4.

Some of these columns require no further grouping, however, two columns do.

The problem is that these two columns are to have a different child group to the other.

So, four columns are grouped by Certification Type ID, of which one column is to be further grouped by Course ID and another is to be further grouped by Certification Passed.

Can this be done? Everytime I try and add the second child group, it has a knock on effect on the other columns.