Sometimes shows will cast actors based on how well the actors did on the auditions and their chemistry with the other cast members, and don't always give attention to their physical appearances when casting for the parts of the family members.

I think those casting the actors for ODAAT did an excellent job on all levels. I noticed that Bonnie Franklin and Valerie Bertinelli had similar facial characteristics that made it plausible for them to be mother and daughter. As for Mackenzie Phillips; where she didn't seem to favor Bonnie Franklin or Valerie Bertinelli , you did get the impression that she could've been the daughter of Joseph Campanella. This gave a more believability aspect of them being a family.

Just an observation that I decided to mention.