Issues with updating using offline repositories for RHEL 6.4 - 6.9

Hello,

I'm managing a bunch of RHEL workstations in an offline network. We have a server running repositories for Base, Updates, and EPEL.
I'm in the process of updating a few hundred systems running 6.4, updating them to 6.9 (don't laugh, these are the cards I've been dealt with!), and a fairly high percentage of them are failing the updates, maybe 1 out of 5 or 1 out of 6 can't successfully complete a full update. For the ones that fail, they get about 10 updates in (out of anywhere from 500 - 1000 needed updates) and the system freezes. When I go to the machine to physically look at it, there's usually something about a kernel panic on the screen, and it'll require a hard system reboot with the power button, to get it back up again.
Is it likely this is just too much of an upgrade at once? Is the leap from 6.4 to 6.9 just too big of a jump?