Two wires into one pin can be done, but it’s a tight fit with large gauge wires. I usually make a “Y” connector with one wire from the pin into a butt connector, then two wires out. It’s less pretty, but easier to do.

I always solder the two together, and then put a short extension on it of a single wire, shrink tube it and add the pin on the end.

Sorry, trifurcon, not pin...

Sort of. The reference to trifurcon is to the small metal piece in your second photo above. Once put on the end of the wire, it sides into that Molex connector, which is the female to the male header pins on the PCB in the backbox.