I think FA sympathy depends a lot on the individual FA...

I was on a recent US flight and the FA was adamant that the family seated near each other, but not together, take their assigned seats and that she would ask the person sitting in the seats in question if they would trade. When one member of that family took one of the seats anyway she scolded them and said "take your assigned seats, I will try to get you all together."

And she was wonderful and got them all together - and even talked a guy in the aisle to taking the middle seat in the row in front.

I wish there were more FAs that would do that - to me the rules are "take your seat and trade before takeoff." There's no "squatter's rights" as far as I know on an airplane...