I have a couple of thoughts. To do the routing simply us an incoming route with the inbound DID going to a ring group. List each of the extensions in the ring group. When someone calls that DID all the extensions in the ring group will ring.
The second part of the question is how to transfer that call once you’ve answered it. Your truck must support more than one call at a time OR you must have a trunk for each call in place. I’m not familiar with your host so I can’t say if they allow multiple calls on a single trunk or not, but you’ll need to know.
Since you can call into 1002 it sounds like your password is correct and it’s connecting. You can dial out from 1004 correctly so it doesn’t sound like a call pattern issue. What type of hardware is used on ext 1002? And is it local on the same network as the PBX or is it remote? If remote It sounds like a firewall problem to me. If local… it has to be a registration issue but it might be above my knowledge level.