RAID5 from a NAS with an unclear array marked as clean, degraded

Hi!
Because I'm a (long time) debian user (and Herbert's Dune fan ) I replaced the original OS of my NAS with OMV : Now, I'm using 0.5.53 on my N4100Pro Thecus NAS. This NAS contains all my pro and personal files and I'm replacing the discs (almost) every 25%.

In short, my two firsts replacements took place under ThecusOS when I reach 25 and 50% of the capacity of my RAID, then, my third change was delayed to 80% and when I reached 90%, I was unable to upload any files on my NAS.
So I used Slax, debian and OMV to tests my NAS and it appears that it comes from the original OS, so I moved to OMV... And I went back on with my third old disc, at this point, I have 2x4TB and 2x1TB in RAID5.

Now, I've reached 95% and I wish to change my last two harddiscs, but I just seen something odd in my RAID management when I changed (again ) my third disc.
In the RAID Physical disks, I can see the new WD Red 4TB (/dev/sdb)

But when I go to RAID management I see two RAID5, one /dev/md126 with the name of my NAS but with a level indicating "Mirror" and the good one under /dev/md127, named N4100PRO...
When I changed the third disc, I assumed that I have to recover with the good one, so I used the GUI, and it worked... almost...

As you can see, now my "good" RAID is clean, but I still see this "Mirror"-thingy and it's flagged "clean, degraded" with no sdb
When I look into the mdadm.conf I see this :

root@GrosNAS:~# grep ARRAY /etc/mdadm/mdadm.conf
ARRAY /dev/md/N4100PRO:1 metadata=1.0 name=N4100PRO:1 UUID=1a12e8ed:41bf690a:fd685af0:2fa21703
ARRAY /dev/md/GrosNAS:0 metadata=1.0 name=GrosNAS:0 UUID=b19d0be0:cafb3ec2:1ef505be:a92fab46

I'm starting to doubt... My first tought was "OK... Perhaps OMV is showing me the "parity part" of my RAID5", strange indeed , but why not...
Then, I see the capacity...
Now, my thought is "Hmmm... Perhaps my ThecusOS was a little more fµ©ked than I had thought..."
I think perhaps it is the "system" part of the old OS, since they used a tiny 128MB Disk-on-Module... Dunno...
I'm quite dubious

My questions are :
Can I remove the GrosNAS line of my mdadm.conf ?
If yes, can I rename the good array with the good name ?
If no... WHAT CAN I DOOO ??

Sorry for the long post, and thanks in advance.
Psy