"Baron Man" wrote:

can one log PIC if another person is flying.

Yes - 61.51 if "acting as pilot in command of an
aircraft on which more than one pilot is required under the
type certification of the aircraft or the regulations under
which the flight is conducted"

what if you're an instructor.

That too allows it

same for twins - if i have a ME instructor rating, can i
log PIC time in an airplane that i do not have formal
training in - but is similar cat/class - piston twin etc.

Yes if the SAME cat/class and a type cert is not required.
I'm not sure what you would consider to be a "similar"
cat/class. It's either the same cat/class or it's not, and
if it's not, the answer is no. As to whether it's a good
idea to instruct in an aircraft you have no familiarity
with, or what the insurance will say, I'll leave that to
others, but you're not required to have logged any formal
training in the models you instruct in before giving
instruction.
Todd Pattist
(Remove DONTSPAMME from address to email reply.)
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