Google Voice Issues

Ok, So I have several google voice numbers,
The first issue I am having is with my main number, if there is no activity for say an hour, anyone who calls gets routed to the google voice voicemail. If I then make a call out, people can call in again, and the cycle repeats.

Second issue:
I have several other numbers, in which I want to specify to a specific extension or set of extensions for there inbound/outbound. But I also want those extensions to be able to receive calls from the main number also.