Halloween is Scottish, there is no way the Americans are claiming that one!!!! We've celebrated that since the Middle Ages.
Mothers Day in the UK derives from the 16th century when Christians would visit their mothers churches on Laetare Sunday, hence why ours is still the 4th Sunday of Lent unlike the US where it is this month. Mothers Day is celebrated at various times around the world, not one for the US to claim either as it derives from various mother celebrations.
I'll give you Fathers Day though
, yep that's from the US. Dads were obviously feeling left out!