My take...and I'm new here.
Welcome to the monkey house.
When I go "to work" and am the seiniro capt. I am listed as the PiC for company stuff (release, flt plan, all that). I am the PIC my partner is the SIC
Sounds good to me.
When I go home and fly as a CFI doing a biannual were both PIC. He is also duel recieved and I am duel given. We have each-others names in our logbooks
You may both be logging PIC time, but only one of you is the PIC, and when an authorized instructor is giving training, the FAA and NTSB consider the instructor to be the PIC regardless of the trainee's qualifications. This is well-established in case law. However, the fact that under the regulations only one person can be the PIC at a time does not change the fact that other regulations permit two (or more) people to be logging PIC time at once. Again, as I said above, you have to separate in your mind the issues of who
is the PIC (i.e., who is the final authority responsible for the flight) from who is allowed to
log PIC time (which in many cases does not require you to
be the PIC).
When / if I act as safety pilot for a friend, we are both PIC. He is flying, I am watching over things. We have each-others names in our logbooks
Again, only one of you can be the final authority responsible for the flight, and that one is the PIC. As discussed above, if you act as PIC for the flight, the regulations on logging allow your friend to log PIC time as the sole manipulator at the same time as you are logging PIC as the PIC when two pilots are required. However, if your friend is the final authority for the flight (i.e., acting as PIC), then only your friend can log PIC time, and you are permitted to log only SIC time. See 14 CFR 61.51(e) and (f) for details.
If I'm doing contract work in a two pilot airplane and I'm in the right seat (not signing for the aircraft) I am the SIC
That's correct -- the other pilot with final authority over the flight is the PIC, and you are SIC. Nevertheless, if you are rated in that aircraft, you can still legally log PIC time when you are the sole manipulator of the controls even though the other pilot remains the PIC.
If I'm doing contract work in a single pilot airplane (king air) I can log as PIC / Duel Received (if the signer of the aircraft has a current MEI),
Only if you are rated in that aircraft and actually flying the plane ("sole manipulator") -- and that doesn't change even if the actual PIC isn't an instructor -- see 14 CFR 61.51(e)(1)(i). Further, that other pilot/instructor will have to sign your logbook for the training you received -- see 14 CFR 61.51(h)(2) and 14 CFR 61.189(a).
or nothing...since I'm not required to be there and didn't sign for the plane.
You can
always log nothing. But then it doesn't count for anything.