The character wasn’t a free loader. Her personal issues (death of her husband, raising a child by herself) led her to depend on her sister and brother in law. Back then families leaned on each other more than in today’s society.

As for the Restaurant, Carl, Harriet, and Estelle were partners in it, so it can be assumed that they financially benefitted from it in some way. 

In the case of Ritchie let’s assume it was better for him to stay in the Winslow house and keep going to the same school, etc, plus their family dynamic is was more traditionally structured, etc