I've found if I just announce "family fun day" nobody feels they can argue with me. It's my default when I hit resistance ;) Eventually the kids cave and agree it's fun ;) I use it sparingly! I don't want it to lose effectiveness.
There could be worse things than having to spend time together picking blueberries. Really, it's blueberries. The family does look like they are having fun...or mocking me. Ok, the teenager is definitely mocking me!