This is so tragic, but I cannot believe they went out in choppy seas in a canoe which is a vessel more suited to navigating rivers and takes a lot of skill to navigate through rough waters. They are very easily capsized. I spent my youth up and down rivers on canoes like this and my parents would never ever let us, or take us out on the open lake with one, too risky. I am sure they probably made that crossing loads of times without incident, but it only takes once.
I feel so sad for the survivors of this, my heart goes out to them. I also used to live in the highlands and I know how cold that water would be. Utterly horrendous.