FreePBX guidance on pin code oversea calls, pick up other extensions, paging and IVR

We need help to setup freebpx with the following functions: 1. Use pin code to call to outstation & oversea. 2. There are 2 different offices. Both offices are using the same range of extension numbers (6XXX). When phone is ringing in the first office, user in second office is not allow to pick up the call. 3. When a phone is ringing, nearby user can pick up the call by dialing a code with the ringing extension. 4. Paging 5. IVR