I call my inlaws by their first names or Grandma and Grandpa if my kids are around.They sign cards and gifts to me as Mom and Dad. I’m not comfortable with calling them Mom and Dad but I am honored they consider me one of their children. My parents are all gone and my H addressed them my first name.
H and I were both born and raised in Ca. Our children call our friends by first name, I introduce myself to their friends by my first name. I have 2 friends whose kids use Mrs and Mr. One is from Texas and the other from South Carolina. My children went to a school where the students addressed teachers by first name only.