Maybe it's my 12 years of Catholic school talking, but I feel that as professionals working in the school, we should address parents/caregivers as Mr., Mrs., Dr., Rev., etc. not as Abby. I always correct the students if they answer the question "who's your teacher?" with "Jones." I have them repeat after me "it's Mrs. Jones." I think that sets the tone for RESPECT in your building.
I think that when you are on a first name basis with parents, as school counselors, you lose some credibility and authority as a school professional. It also sets a clear boundary that we are not friends, but school personnel.
How do you address parents and how you do have them address you?