Unless the blockages are from something else entirely (unlikely), they should probably test the kids' blood for familial hypercholesterolemia (high blood cholesterol that runs in the family, as opposed to diet.) DH's father had a heart attack many years ago, DH was tested and already had high cholesterol in his early 40's, his daughters (barely in teens) were high as well.
His father passed away several years ago, but DH and the girls (now women) take their meds religiously.
I'm adopted, and I've never been able to decide if that means that I should worry about what genetics are ticking away in me, or not worry at all.