Do you need a suitcase each?
I've just been to measure our biggest (remaining) case, and it's 68cm - which is a size down from yours. I have to be careful not to overfill it.
We had a bigger one (possibly one size larger than yours, but I'm not sure), and I got 40kg in it. Luckily I tried to move it, and stood on the scales before we went to the airport. It was filled with a slightly weird combination of stuff, as we lived abroad at that point, so had quite a few shoes, books, dishwasher tablets (don't ask!), marmite and other such none typical holiday packing items.
We will only take 2, maybe 3, cases between the 4 of us this summer.
So, in summary, yes, you've got far to much suitcase space. I'd send at least 2 back, and get smaller. That gives you flexibility in what you take other trips as well.