There is no need to have two instances. You can achieve that with one instance and configurations.
If you use FreePBX or similar, then you can create separate groups in the FOP2 Manager, including the buttons you want displayed in each group. Then edit your users and assign only the group you want them to see.
If you use a multi tenant system, then you can use context isolation. It is done by default on supported backends (MiRTA, Elastix MT, Thirdlane). With panel contexts, you not only will have separate views, but also separate users (so you could have extension 100 on context A and extensions 100 on context B, being each one separated from the other).
You do not give specifics, but I think option 1 is just fine for your purposes.
Best regards,