Best Way to Add a Terminal Between Two Wires?

I suspect I am using the wrong terminology when searching for this. Or over thinking it... I have two 16awg wires with terminals on the far ends and are just cut on the ends of interest. I want to join them but I also want to add a 3rd branch. What is the best way to do this? I essentially want a 3 terminal jumper. The two 16awg wires have factory sealed terminals I can't mess with on the ends and the 3rd middle one will be a metri pack 280 female. With the cable seals I don't think I can use the MP280 as the join itself like I could with a normal bullet or spade terminal so looking for the cleanest alternative.

If I'm understanding you correctly you could solder the 3 wires together or you could use a terminal block https://www.homedepot.com/p/SPT-8-Way-Terminal-Block-Bus-Bar-15-TB01A/308017056 they have endless types of these so you can look them up to find one that suits your needs. Also Mobile Solution has them with fuse holders if you want one that's a little more fancy.

Thanks and sorry for the delay in response. Yep, you understand correctly. Soldering and heat shrink look like the way to go as I am trying to keep it in a harness.