The broken mechanism knocks value off the cheaper part of the set - i.e. the mum - maybe $8-10 off her price. That assumes the door is still in place, just that it no longer closes (this is really common with this item).
As for the babies, they are very very easily scuffed from general play wear so minimal wear does not dent their price too much. Also as they are so hard to find so a lot of people are happy to accept a little issue.
How bad is the damage?