@Boris_yo The best solution remains: have them all store any data to a central file server. This central file server should have enterprise-level hardware (i.e. very reliable), preferably some form of RAID for any disks, and daily backups.
If you really want to take full system images over the network at the same time only once a week, use any scheduled backup application. But, I warn you: network performance (and "external storage device" performance) will be terrible if they're all writing at the same time. And full images include a lot of cruft you don't really need. And losing up to a week of data is terrible.
Losing a week of data for many businesses could actually put them out of business.