I lost my mom in January. And my cousin in August.
Because of my personal experience of my own grief, and because of my interactions with my grieving aunt, my personal choice would be to write a letter.
Dear Aunt X and Uncle Y:
I've been thinking so much about Friend lately. I remembered that thing he did that made me laugh. We were 8, and I think I just about peed my pants--that's how funny it was. Isn't it odd that we don't laugh so much as adults? It was so much fun growing up with Friend. It was like a big, huge family. I miss him still.
Then a couple of days later, I found this Polaroid. Look how young my handwriting is! And how young he is! I can still see him in my mind, running around in the backyard chasing the dog to get the ball back [or whatever he was doing when the picture was taken].
[insert any other memory that has come to mind in the last few weeks, especially if it's good, or particularly indicative of him or of your relationship/closeness with him]
Sometimes it hurts a lot when I think of him, and sometimes I forget that he isn't here anymore. He was such a closely-woven-in part of my life and my identity, I can't really quite internalize it most of the time. In some ways I find it comforting, that I forget we've lost him. Because it reminds me that I haven't lost him. Not really. He's always part of me.
And sometimes it hurts so terribly, terribly much. And I've found that I treasure that, too. Because it shows me how much I love him, and how much I've lost. It reassures me of the value of my friendship with him.
I thought you might want the picture, so hold onto it. And hold onto the thought that he loved you so much, and that you gave him such a wonderful life. I'm always grateful that you gave him to me--that you made me and him a part of the same big "family."
I know it's the anniversary, so sometimes it's going to be extra hard for you. I wish I could be there to put my arms around you. When you need a hug, think of me, and imagine me hugging you.
Lots of love,
But I wouldn't send flowers. I think that would dilute the power of a letter like this.
As for what to say when it's a potentially guilty situation (suicide; maybe he drove while impaired and they didn't stop him; maybe they didn't push him to seek treatment for some rapid illness), I would completely ignore it. It doesn't matter. It completely doesn't. You've all lost him. The [cause of death] doesn't negate the times and the closeness that came earlier. And it doesn't negate the pain of losing him.