You can never have to much electronics. Keep 'em all - get more later. If he’s really lucky he can find a broken one or two of the same model for “spare parts”.
I would say the two 20s can probably go. I can see needing both the 100 and the 400 for some things. If you can talk him into that, you gain ground on him–there’ll be one less scope in the place.
Of course, I wouldn’t get rid of any of them, but I’m a serious packrat. I have electronic widgets I built when I was a kid stored around here somewhere.