Cross redirects - how to fix?

Question

Telephony

There is telephony based on Cisco 2851 with Cisco Unity Express installed, but with a broken web face, so that management is only through the console. There are two numbers on it, say 101 and 102, each one has a city number like 1111 (additional). Each is configured with call-forward busy redirection to the second number. As a consequence, if both are busy, the call rushes between them until the timeout. I would like that in the case of both busy numbers, the call went at least to voice mail (say, 800). If the number does not answer, then forwarding to 800 is already configured, call-forward noan 800 timeout 25, on both numbers. How can I configure these numbers so that, firstly, when dialing 1111101/102, the call first gets to 101/102, if it is busy, then to the neighbor, and if both are busy, then to 800?