Switch from Delta to Omega Preview

which one , i see upadte preview omega and update preview delta?

If you are part of the Insiders preview program, consider going to a ring which has less frequent updates, like Delta or Omega.

Alternatively you can unenroll from the program, so you only get GA (General Availability) updates when they are released.

Only offering omega, there is no delta option?

If you are part of the subset Alpha Skip Ahead preview that has the new Dashboard, use the Insider Hub and Manage option to change to a lower preview ring, eg Beta, Delta or Omega.

Or opt out of any previews and unenroll the console from any previews and install the General Availability public OS.

Be aware that changing previews or opting out will require a Factory refresh of the console. You will need the account details of any profile that uses the console.

In my understanding the Dashboard experiment, A, B, C selection, is totally random.

As "Both consoles say their OS Version is (19h1_release_xbox_dev_1911.191028-1335)" your consoles are either in the Beta or Delta ring.

Both those rings and Omega ring are getting a preview update News release notes Beta Delta Omega
Insiders today, which you can manually start or wait until it becomes mandatory.

After you do the update, if you want to change rings, it will be the perfect time to change as all those rings will be on the same release. Subject to eligibility.