Small technical comment for pilots.
My only real experience with this general type is the PA23 - don't know about the Chieftain.
Two piston engines and two tanks in each wing with a changeover cock for each engine.
When wishing to use all fuel from a tank I'd change one engine over to full tank whilst it's tank was still showing fuel on the gauge, check it continues to run, and then carefully watch the other engine. When the other engine indicates fuel starvation change it over to its full tank and observe for five minutes.
Then put other engine back on almost empty tank until fuel starvation indicated and switch to almost full tank.
Not a good idea to run both down simultaneously.
I'd only do this at a quiet period of flight and only if necessary. Pax didn't like engine splutter.
Sorry about your cousin, MLP, sounds as if he almost made it.