My heart breaks for this family. However, I can't help but question why the parents continued to have children after the first one was diagnosed. It was a genetic issue, I'm sure their doctor informed them that it was possible future children could be affected. 
This is purely my opinion. Why create human beings when their existence is just going to be full of pain and sickness? 
When I was pregnant with my one & only child, I was diagnosed with cervical cancer. Fortunately, I was able to have a successful pregnancy and a healthy baby. Shortly after, I had a complete hysterectomy instead of lesser procedures. My doctor asked more than once if I really wanted to go through it just in case I wanted more children. My feelings was that I wanted to make sure I was alive to watch my child grow up, if I wanted more kids that badly, there are millions of children in this world already that need loving families.