I guess it’s all single disks…and no backups? …risky business…even more so with these 16+ year old ancient NAS devices.
Take the disk out of the NAS and read the data in a Linux PC or ext reader in windows.
Implement a storage strategy on a new device that can handle arrays of more than 16TB and implement RAID5 or higher and don’t forget your backups. (no more sweating when disks fail)