Nasilsin and nasilsiniz mean how are you
You can say nasilsin to your friends, family and people you know
You say nasilsiniz to people you dont know, manager etc
Foi o que um nativo me respondeu
Nasilsin is personal pronunce 2singular.
Nasilsiniz are personal prounce 2plural
but if the one you talk is important
For example, president
You must say nasilsiniz even if this is one person
E outro nativo complementou com mais essa informação, espero ter ajudado!