Your family sounds like mine Maz. The way my mother dealt with it really turned me off the whole Aunty Uncle thing.
The reason I don't like it is that it creates a barrier to my way of thinking. Though I can see the way you are explaining it it marks a boundary for really special people in your life. I get that.

I find mail addressed in the past to Mr & Mrs DH very very uncool... though I also know it was the done thing. I am me I am not Mrs DH... I never used the MRS thing... I have always been just my name.