Ring Group and Voicemail / Ring Group if no answer / busy

This is what I need to do, but not sure I have it working or not.

(1) I have an AT&T line that does a roll-over after 3 rings to an internal ring group <let’s call it RG1>.

(2) If busy, want RG1 set to roll-over to RG2 ASAP.

(2) If busy, want RG2 set to roll-over to RG3 ASAP.

If RG1 is not busy, then after RG1 rings for 12 seconds, go to Voicemail, ie, bypass the remaining ring groups.

Is this possible? I cannot really test it here at work since everyone is working.

Thank you in advance.