what's your exact issue, call gets disconnected or not going to correct voicemail ?
Call flow is as follows: Auto Attendant--->option 1--->hunt pilot-->no answer-->DN on receptionist phone--->no answer--->different DN on receptionist phone-->no answer-->voicemail.
For the above scenario, for calls to go to second DN's voicemail you can use below solution.
Use Last (Rather than First) Redirecting Number for Routing Incoming Call:- Enabled
To learn more regarding the option enabled go through below link.
https://www.uccollabing.com/unity-connection-last-redirecting-number-voicemail/