"Get a Jetprop. Getting 6 adults off the ground in a Seneca will be "interesting" with sufficient fuel to actually go anywhere. A Jetprop however will fulfil your needs and you'll wonder why you even considered a piston twin."
Have you ever done the M+B on a JetProp?? Usually, full fuel means about 40 kg below max. ramp mass - the pilot may not even enter the plane legally before dumping some fuel. Hard to be legal on any mission with 3 + adults and IFR reserves. Not to talk about estimating the exact amount of fuel in the tanks.
My Seneca III offers 382 kg with full fuel (123 GAL). Electronic on demand oxygen (6 seats, mountain high), no A/C. Aircraft fully loaded including RDR-2100, TAS620, WX500, full copilot instrumentation, FIKI, air data computer, and so on. The Seneca V with factory oxygen will be about 100 kg more heavy (electric flaps, more comfortable interior, oxygen, ...).
Over mountains, at night, during solid IMC down to ground or over water I would always prefer a twin. Of course, I'd prefer a Conquest or Cheyenne I, but those are way too expensive for me.
A Meridian offers much better payload than the JetProp, comparable to the Seneca V.