And yes Vestalink said to open total new account with a new number, I don't see a sub account option at all.
Based on your OP you don't need a new account or a new number. Vestalink does not support sub accounts but they do support multiple simultaneous UAs registered to your account.
You don't need to use the same ip address, you need to use the same SIP credentials. You should be able to set up your second Obi the same way you have the first one configured.
Disclaimer: At least that's the way things worked at Vestalink when I was a subscriber a few months ago. Things may have changed since then.