I read somewhere in this forum that UA will actually upgrade companions in advance along with the elite member. Not sure if that's standard procedure, though.

And (as applies in my scenario) what happens if there are 2 FC seats available and not, say, 4? Does no one get upgraded -- or do they give my seats away to a lower-status elite?

And if I split off the non-plats, does that mean they're no longer eligble on UA for "companion" upgrades at the airport?

This is just way more complicated than it should be!