Later on reading another comment about ratio of shooting / workflow, brought a lot of sense into why picking those two.
As you can go into a room and do the initial wide with the 18 then you'd do heaps of mediums and close ups with the 35 and 70, so only one lens change.
While using say an 18-50 and 85 could lead to needing to do many more jumping back and forth lens changes.
