“Mentor,two of whose brothers attended primary school,wishes to be an artist.”
You are correct to use whose instead of whom but I would phrase the sentence slightly differently.
Check out the rephrasing of the sentence below:
Mentor, whose two brothers attended primary school, wishes to be an artist.
Remember “whose” is a possessive pronoun that is used to show possession of something or to find out who owns something.
- The Smiths, whose daughter attends the local high school, have decided to donate money to the new public library as they know it will benefit their daughter’s education.
- “Whose car is parked on the double yellow line? It will be clamped if the owner doesn’t move it immediately” the traffic warden warned.
“Whom” on the other hand is an object pronoun and is often used like “him” “her” or “us” or to ask which person received an action.
- Whom did she write the letter to?
- I don’t know whom is coming.
- Whom is he going to fight?
- I know the man whom he is going to fight.
- Whim did they interview for the position in work?