Another is that the latest EF version of the 24-70 f/2.8 (the Mk II) can be had for about half the price of the RF version (where I am at least), so there's probably a good $1000 to be saved at the outset if they go with the EF Mk II.
Canon EF 24-70mm f/2.8L II USM (or perhaps a 16-35 f/4 or the new 24-105 is ii) Canon EF 70-200mm f/2.8L IS II USM; Keep the Canon EF 50mm f/1.4 USM due to f/1.4 which is occationally handy; I like this idea! Might be nice to keep the 100-400, but you could also just use a 2X Extender with the 70-200. PHFNz.