Even if you do manage to get both of you into F, I've found that there are often A-holes that refuse to switch seats with you so you can sit together. This has happened to us several times and always ruins our day.

When traveling with my sweetie, if we can't confirm both upgrades and that both F seats are together before boarding, we request to be put together in the back. The upgrades to us matter less than sitting together which appears to surprise most gate agents.