" "We would like to express our sincere condolences to you and your family. "Words cannot express the depth of my sympathy for your loss.Wishing you strength and comfort as you navigate through this profound grief." Keep the letter as brief and as short as possible. Please accept my deepest condolences. I would just write something simple. I'm sorry for your loss. "I'm so sorry to hear about this" is fine. You can also add a "I'm thinking of you and your family". Be sincere and express your feelings of sympathy.