You cannot have the Catalog file including related Previews and other data files on the NAS. They must be on a physical connected disk drive.
It's ok to store the original image files on the NAS.
You can install Lightroom Classic on two Computers with only one in use at a time.
A Catalog file can only be opened by one Lightroom Classic application at any time.
Regards, Denis: iMac mid-2015, 5K 27”, GPU 2GB, Ram 24GB, HDD 3TB, macOS 11.7.6 BigSur,; LrC 12.3, Lr 6.3.1 Ps 24.4.1,; ACR 15.3,; Camera OM-D E-M1