Lol… this explains the frankness in my family…with my elder grandparents calling each other by their first names in front of everyone…and then my parents do the same thing as well. They do joke around a LOT.
I still remember going to visit my nana and nani in Pakistan and hearing convos like this: my nana jaan would be heading out the door and I hear my nani screeching from some back room “Oyeee xyz (nana abu’s first name)… tu kithay ja raha hai!!! Naan wapsi pe le aanaaaa!!!” Then my nana would yell back respond “sun leya… naan ley ayoon ga… saara mahale ne saadi begum ko sun leya hai!!! naan main na boolna wala!”. 
Their interactions were hilarious… it carried on to their kids and the way they talk to their spouses. Mabey thats why I was I found this topic to be so intriguing… formal and informal doesn’t exist in my family!! More like frankness ki ek haad hai!!! lol.