How to move the root partition
You’ll need to boot from a live cd. Add partitions for them to disk 1, copy all the contents over (with rsync, see rsync clone partition), and then use sudo blkid to get the UUID of each partition. On disk 1’s new /, edit the /etc/fstab to use the new UUIDs you just looked up. Updating GRUB depends on whether it’s GRUB1 or GRUB2. If GRUB1, you need to edit /boot/grub/device.map ...