How to setup lines properly

Ok I need some help. I have 4 pots lines connected to a GXW4104 (fxo gateway). For each phone we need a type of button for each line. How would I set this up Properly? Right now I have it setup so the fxo gateway has an extension for each line and setup as a sip trunk. From there I setup a custom trunk to dial SIP/82 for example (82 for the line I gave the fxo( There is a entry for each line in the fxo under “extensions” and also under “trunks”)). From there I setup the phones to use blf for the multi purpose keys. We used to have this really old nortel bcm system.( no one knows how it worked.) With that there were buttons on the side for each line lets say line 1 for example that when you pressed that it would connect directly to that physical pots line. no dial plan or anything just the physical line.

Did I set up this properly? It seems like I did not do it right. It “works” but does not seem right. Also if a user puts a call on hold only that phone can pick it back up, it it possible to share a line? Not call parking.
Also The phone line hangs when someone hangs up on voice mail, any ideas why?

I guess the main point is how do we get it so that there is no dial plan, the user just picks the line? (they are all different businesses)
Thanks for the help

Phones: GXP2000