Rohan is married to Anjali, and they have a son named Arjun. Rohan has one brother named Nitin, who has two children, Priya and Vijay. Anjali has a sister named Kavita, who is married to Sunil. How are Sunil and Vijay related to Anjali and Arjun, respectively?

Respond very briefly.
Sunil is married to Kavita, who is Anjali's sister. This makes Sunil Anjali's brother-in-law. Regarding Arjun, since Kavita is his maternal aunt by being the sister of his mother Anjali, Sunil is Arjun's uncle by marriage, hence also referred to as a maternal uncle in some cultures.

Vijay is the son of Nitin, who is Rohan's brother, making Vijay Rohan's nephew. For Arjun, since Vijay is the child of Arjun's paternal uncle (Nitin), this makes Vijay Arjun's cousin.