I can get into initramfs on that drive now, but the first thing it says is "no root device specified. Boot arguments must include a root= parameter". I assume I'd add that to GRUB, if I could see the OS in GRUB!
Then from the BusyBox initramfs prompt, i try vgchange -ay to try and activate the LVM partitions....? , and it activates three logical volumes from each of the two Debians. I figured out that I can pass it my correct LVM group, and it only activated those three. I exit from the initramfs Prompt and it says it can't find some files in /root/proc, then it hangs forever.
Man, all the stack overflow stuff I see says things like "mount the root to a new folder, then fix the problem, then reboot." But doesn't ever explain how to actually do some of it. I'm just too new to follow the "yada yada"!