Can I say “ My deepest condolences for your loss” to another family member?

My grandpa died and my aunt ( wife of my brother , dad ) text me letting me know he passed away. I don’t really have communication with my dad side of the family only with my her and my uncle

I appreciate that she let me know but I don't know what to tell her :( i don’t wanna sound rude I’m thinking of sayinh.

hi aunt My deepest condolences for our loss of my grandpa but I don't know what else to say.

Can I say “ My deepest condolences for your loss” to another family member?
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