Personally, if I were you and you have the Avios just go for it but only First out and staying put in CW coming back which a relatively 'short' long haul flight. My own view is life is too short so look at it as a special treat perhaps?

AIUI there's no difference in cash, as in any extra taxes to pay, to UuA and going to the east coast USA is not a lot to spend Avios wise for the three of you and will give you access to the CCR etc. Quite a few years ago now but I have taken my Son in F a few times using UuA but it was worth every moment and I have very fond memories of those trips.

However as always YMMV and you'll get a range of opinions of FT