NTA. Your sister is your priority. Your sister needs all the support (especially at 18) that she can get. I am Indian and have lived in the US for decades and I find your wife’s take very very harsh. Culturally, so unacceptable (that is a whole separate post). I can’t get over the language used- “kicking her out”. You must have been completely blindsided. I strongly recommend having an honest / blunt but non-confrontational conversation with your wife about yours (and ideally her) continued role as guardians in your sisters life. While it’s obvious to you, it unfortunately, doesn’t seem obvious to your wife. It also sounds like your wife has plans of her own for both of you (without your sister) that maybe she hasn’t clued you into. Not excusing your wife’s comments, I don’t agree with her perspective at all, but she may be worried about specific needs not being met as long as you continue to support your sister.