Auntie and uncle for non relatives?

What are your thoughts on calling people “Auntie/uncle __” ? That aren’t actually yours or your partners siblings?

To elaborate I have 2 best friends, one from high school and one from university. They’ve always been like sisters and therefore my children refer to them by Auntie. We also live in a duplex farmhouse with a couple in their late 50s, and no children of their own (not really relevant but the love they have for our kids can’t even be put into proper words). They have been here since my first born was 8 months old and my seconds entire life thus far. They are VERY much involved in the upbringing of our kids and therefore we also call them auntie and uncle. My husband has a sister and I have 3 brothers. So them and their partners of course go by the same terms.

It was recently brought to my attention by my MiL that this is too confusing for my children and we should only be referring to our true siblings as their aunt and uncles. I did not come from a good family so as far as I’m concerned your family is who you decide is your family, blood or not. But now I’m questioning if this isn’t a healthy habit for me to project onto my kids? Thoughts?