Trouble binding harddrives using mhddfs in /etc/fstab

[mahesh]

Hello Amazing Ubuntu community,
I'm fairly new to this arena and I've gotten myself in a pickle.

I have two 4TB harddrives installed on my computer; however, only one (/dev/sda2) was initially mounted.
Following this tutorial, I tried to bind my two hard drives to my home directory so that I had "one" 8TB directory.
I created two new mount points: /mnt/ext1 and /mnt/ext2. Successfully reformatted /dev/sdb1 and mounted it at /mnt/ext2. However, /dev/sda2 was the HD I had been using up until this point (4TB HD full) and it was mounted to / . When i tried to 'umount /dev/sda2' I got the error that it was in use. I searched online and found an answer that if I restarted my computer, the HD would no longer be in use and I could unmount it.
So, you can imagine what happened, I restarted my computer with the /etc/fstab file already configured for the new mounts and binding. And I've been stuck with Boot Failed similar to this post.

Following some advice, I've been able to install Ubuntu on the /dev/sdb1 drive and get access to all my files. But now I have two Ubuntu installations with two different computer names etc. I want to use the original one because I already have a static IP address that I can ssh into. Where do I go from here?

Here is the Boot-Info Summary: https://paste.ubuntu.com/p/f3QTDdXxWy/

The goal is to successfully get the two 4TB HDs binded on the / directory using my original Ubuntu installation. Thank you for any and all advice.
-René