For the third exercise, I used a shared parameter to do variations of the width between mother and child.
I made first a child with a rectangular geometry with the width as a shared parameter.
Then I loaded it into a mother element, also rectangular. Here I wanted the width of the mother twice the one of the child so I indicated in the family type window "S_width mother = S_width*2".
Then I created an assembly of this element in which mother and child where linked each others. I puted them as they could be assemblated each other and fixed them using reference lines.
Then I played on the variation of the width and saw that mother and child evoluated together.