How to assign approval group in vacation rule set up or any possible way to select approval flow

Hi All,

Client has below requirement for the order approval rules.

Normal Scenario → Route to User A

If User A is on vacation or business trip → Route to Approval groups which has User B and User C set up as parallel approvers.

We have explored the vacation rule set up in BPM worklist, but somehow the approval group selection is not available. It is showing some groups that are not the approval group in BPM. What type of group should we create to be available here?

If this does not work with vacation rule set up, is there any other workaround to achieve this requirement?