When I am in these situations, I do one of the following:

A) Buy Coach tickets for the three of us (keeping one on my PNR) and assuming I clear along with my companion, I upgrade the remaining person with miles.
B) Buy First Class tickets for the three of us using money or miles.
C) Snag a row in Coach and be happy there.

Now, with the understanding that I've never done what you're attempting, here's what I see as your options given that you apparently have an F ticket that's paid for one way or another and it's apparently difficult/impossible for you to downgrade it:

1. Keep your seat and wish your SO good luck with the kids.
2. I would preboard with your family since you are all traveling together and once onboard, mention your plan to the FA (making sure they understand it isn't an upgrade but a purchased F seat) and then head back to coach and take the middle seat. Then, I'd offer your FC seat to the middle seat person (although they will likely be one of the last to board).
3. I suppose you could also ask at the gate if they could downgrade you and assign you a seat with your family thereby freeing up your FC seat for an Elite. It seems that GA's are capable of performing miracles of all kinds (assuming they want to).

Maybe another FTer in your same predicament or US employee could unofficially address your situation. Generally speaking, it's been my experience that cabin crews and fellow premium cabin passengers dislike people going back and forth and/or sending food back and forth to Coach so hopefully you can find a solution that won't cause that.

Just offering my 2c.