I want to do mutah, with conditions, with someone, to get to know him. My dad and grand father passed away.

I heard that I dont need permission from anybody. It still be a halal relation. But I also heard that I need permission from my guardian.

What is the fiqh law please?

by

I really appreciate your intention to avoid haram.Praying for the maghferat of your father and grand father.
Yes please get permission from your guardian for Mutah and Nikah too.