Are they networked (wired)?
What I did for ours as I needed to update them all since for menthe Jessie to Stretch didn't go well on any of them.
Pi3's lost WiFi at some point and SenseHAT went a bit funny. (Led array and would stay on at the start and shutdown etc).
So popped the SD cards one by one into the adaptor and just copied the files into separate folders as backup.
Then started afresh with stretch, got it setup etc moved all the folders used, documents, desktop, random places over to it and then cloned that SD card card to all the others.
BUT if I had these all networked (they are not) via wires, then do what (royal we, John Witts really) did at the PiJam Hull and setup a PC with PiServer. It so much easier now, each child, adult, pineapple has a logon and the files are all kept on the PC (laptop here).
Only one 'image' to keep up to date and that's it.
Something to look into if you can make use of it.
It stops this sort of mess.
Given you didn't have Chromium, they are old old images of Jessie (like I had), you may need to install a few other things as well. (Gpiozero for instance)?
Which Pi's are you using Pi2/3?
If it the B+ or earlier then chromium isn't going to be fun.