I grew up that it was respectful that my aunts and uncles are to be called aunt and uncle. as we got older we’ll say their first names but thats a rare thing. That’s how it always was in my family and thats how it will be with my kids iy”h. I myself do not have siblings but my husband does so his siblings will be aunt and uncle. yet, we have friends and since it is not respect for them to call them by their first names they will be known as aunt and uncle(since they are close with us).
It’s all about respect. the problem with first name basis is that you loose the fact that people are older and that you need to have respect for them and not be chummy chummy(if you know what i mean)