Question: Why does Hank call Pat "mother"?
Question: Does Ray ever stand up for Debra when his mother insults her?
Answer: He does eventually when Marie teaches Debra how to make her meatballs, but changes the spice label.
Answer: Unlikely. It's shown numerous times Ray is scared of upsetting his mother.
Answer: It's something which some more formal / conservative couples do, possibly just as a byproduct of having kids and using a consistent reference.