In the Teams admin centre -> Calling policies create a policy and activate "Busy on busy is available when in a call". This will prevent you from receiving a signal 2nd call (also on 2nd device) when you are in a call.
https://admin.teams.microsoft.com/policies/calling
You can then link this policy to the desired users.
You can find more detailed information on the distribution of Teams Policies via this link.
https://docs.microsoft.com/en-us/microsoftteams/assign-policies