Operators are not be able to use /op and /deop commands. There is no way to change member permissions via commands. OPs should be able to manage player rights so they can change a new member from visitor to member with commands.

Reproduce the problem:
Start a new survival realm with 3 players (playera,playerb,playerc) with cheats OFF. Player A being the owner, player B being operator and player C is visitor. Try to change player C to a member using player Bs account.

Expected behavior:
Player B issues the command "/op playerc" and player C gains member rights.

Actual behavior:
Player B issues the command "/op playerc" and receives error saying "Unknown command: op"

Now even the owner has access to this command so the only way to change player rights is through the realm settings.