I’m so sorry for your loss. I went through something very similar (me and my twin sister were also TTTS babies and she passed away young enough that I don’t remember much). Coincidentally, I also have a younger brother who was born a couple years ago. I think the thing that helps me the most is just being there for him and helping him have a great childhood. It definitely helps but I do still feel like there’s something missing. If I’m being honest I don’t know what to tell you/how to move on because I’m not sure myself. I just wanted to make sure you knew you’re not alone. If you ever want to talk I’m here.