Raj is married to Priya, and they have a son named Arjun and a daughter named Diya. Priya has a brother named Akash who is married to Nisha, and they have two children named Vivek and Isha. How is Vivek related to Raj, and how is Isha related to Diya? Also, why might Arjun and Vivek look alike?

Respond very briefly.
Vivek is the son of Akash and Nisha. Akash is Priya's brother, and Priya is Raj's wife, making Akash Raj's brother-in-law. Since Vivek is Akash's son, this makes him Raj's nephew.

Isha is the daughter of Akash and Nisha, making her Vivek's sister and since Akash is Priya's brother, Isha is Priya's niece. Diya is Priya's daughter, so both Isha and Diya are daughters of siblings (Akash and Priya). This makes Isha Diya's cousin.

Arjun and Vivek might look alike because they share a common set of grandparents from Priya and Akash's side. Since siblings often share familial traits, it is possible that their children (Arjun and Vivek) could also exhibit similar features.