Let the thoughts come out when they are ready.
For me, they often pop up at odd moments, not anything like when I expected them to. When I'd bang my elbow so hard it made me cry, when I took a long walk and got thoroughly exhausted, when I was suffering from insomnia and not entirely reasonable....... those are the times when I'd have some interesting breakthroughs. It's like.....when I let my guard down? Something like that.
Your job isn't to force yourself to feel things -- just to be the scribe when something tells you it wants to be written down.
Btw, I too have a mentally ill brother, and I write to him too.
Hugs,
GL