How these clauses are co-ordinate?
Solution 1:
Your first two examples have nonrestrictive relative clauses, so called because the relative clauses do not restrict the reference of the NP they go with. In these two examples, the relative clauses are not modifiers of a noun, because they do not give information that is required to figure out which individual is being referred to.
In the third example, however, "who broke the window" does restrict the reference of "boy" -- it's not just any boy, but specifically the one who broke the window. Now, the relative clause is a modifier of "boy".