Drobo capacity critical

Good day all, I do hope someone can help me with this issue.

We own a Drobo 5N with 8 TB (4X2TB). The machine indicated that it is full, and we added a 4TB drive in the open 5th slot, now with a total of 12TB. It still indicated full (7.09TB) and then we learned that we actually needed to install 2 (two) larger drives to have any effect. Then we replace the one 2TB drive (indicating red) and installed another 4TB drive therein, but it still indicates it is full at 8.92TB. No another old 2TB blinks red, again.

As far as data consumption is concerned, it should be impossible. We have a very small admin office operation. We recently moved our most frequently used core documents to cloud (OneDrive and also iCloud) The total space we use on cloud is 14.7GB of 1TB available.

The previous setup was done by an IT person where we wanted to auto backup 1 x iMac, plus 2 to 3 PC laptops. Although there could be a lot more data than the 14,7 GB on cloud stored on the DROBO, it seems impossible to reach the maximum on the Drobo with only the four computers. The collective space on the individual drives is far less than what was available on DROBO, even at double the capacities.

It may be possible that it duplicated the backup etc., however, we dont want to loose valuable financial data.

HOWEVER, when we look at event (attached) then it says FREE SPACE 8.73 TB (97.97%), USED SPACE:185.94GiB(2.03%). We are lost in the IT world.