Years ago, my mom had told me that in February she would be caught off guard by her feelings of being down until she looked at the calendar. She lost both of her parents in February (different years, but both in February). I never understood what she meant until this year. And it wasn't November (the month my dad passed away), and it wasn't March (my dad's birth month), but June, Father's Day weekend.
When you go through grief and come out on the other said, you are never really done grieving, you have just learned to live with the loss. With everything that I went through, I have used my grief to understand what to do, and more importantly what not to do when someone else is grieving the loss of a loved one.
When I grieved my dad's death, I had to come to the realization that he wasn't going to be there for any of my children's graduations, weddings, etc. (he didn't get to see any of his grandchildren get married for that matter) and I had to be ok with that before I could move on. One of the obstacles that I had to get through was the age my twins were (5) when he died and that frightened me...they would never really know my dad. I say that because I was 5 when my grandmother died and I don't know much about her at all. Another friend of mine told me that you can keep them remembering your dad through photos, and stories. (I really do have smart friends! LOL)
I had another friend once tell me that it doesn't matter if I lost my dad too, the relationship between us was different than the relationship you had with yours, so honestly, I don't know what you are going through. No one deals with death the same way. No one knows how it will affect someone else. The only thing you know for sure is they are hurting in some way. And there will be days that they seem absolutely fine, then there will be other days that it's not so fine. Somedays it hurts!
I don't have the answers, but what I can tell you is that if you have a friend who is grieving, let them talk. You may hear the same stories of their loved one over and over, but it gives them comfort to be able to share their stories with you. Just because they are gone, they aren't erased from your memory.
If you have a friend who is down, ask them to tell you stories of their loved one. I know they would love to tell you, but don't be surprised of a few tears fall. It's ok...grief does that. As time goes on, the tears will be less, and the smiles when the stories are told will be more.