Malayali chechi

Hi everyone,
I need some advice regarding how to address my brother-in-law. He is 2 years older than me, and I was asked to call him cheta. However, I have cousins who are 5 to 8 years older than me, and I address them by their names (or bro). I do call my elder cousin sisters chechi, but growing up, I spent a lot of time with my cousin brothers and always called them by their names or nicknames.
Now, it feels a bit strange to call my brother-in-law cheta. I'm considering asking him if I can call him aliya instead, but I'm not sure if that would be considered disrespectful or if my wife's parents/relatives would be okay with it.
I just want to clear my mind, as I keep wondering why I'm calling him cheta and it keeps bothering me all the time. I'd love to hear your experiences and advice on this matter.
P.S. I often use cheta casually with strangers on the street, so I'm comfortable with the word itself. It just feels odd to use it with someone only two years older than me.
P.P.S Background - i was born and brought up outside kerala in another city. And all my relatives live in this city (yes Im a malayali).
Looking forward to your thoughts

What do you think ??

As y’all can see I’m really interested in these geographical variations, so
Is there any other term?
I’ve heard tons of terms for elder sister in Malayalam
Chechi: most malayali usage
Chetathi: some thekkans
Echi: malabari
Etathi: vadakan
achayathi: certain thekkan cristiani
Akka: elderly Trivandrum folk
Itha: most Muslim
Icha: Kasargodan muslim
Oppol: certain caste communities
Jaishtathi: formal asf
Is there any other term that you guys have heard?

I'm in my later 20's, recently joined a Malayali association where I live. And I'm not really sure what to call the people in the association. When I was a kid, it was really clear-cut who was a chettan and who was an uncle.
Now, it's grey.
My current standard is if they call me mone, they're an aunty or uncle. Otherwise, chettan chechi.
But it's confusing. Like someone that I called aunty, calls someone whom I call chechi, aunty.
How do you all decide?

Hey! I'm an dentist who was born and brought up outside of Kerala (In India), recently i did move to kerala and do own a specialised clinic here, I'm a 27 year old woman and have it has got me curious how many malayalees address me as chechi, instead of ma'am or doctor, it's especially men who are my age or maybe a tad younger (late teens to mid twenties), who tend to do this more often. Have never experienced this where i grew up, is it a thing here? Do people refer to male health professionals as 'chetta' as well, or is it more used to address women, or maybe it's just my experience? I am normally very friendly with people, look younger for my age, and i could probably give off an older sisterly kind of vibe, so maybe those have something to do with it?
Don't get me wrong, 'chechi' is very sweet and i don't mind it, just curious if it is just my experience, or a Kerala thing.

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