I feel ya. I miss both my mom and my sister too. Yeah try to remember the good times. Maybe write your dad a letter. Sometimes I write my mom and sister a letter.
My mom has been gone 15 years this year, and it doesn't seem possible. In three years I'll be older than she was when she died, and that also doesn't seem possible.
I lost my Ma over ten years ago. My Pa went a few years later. It's daft at my age to talk about being orphaned, but it does feel a bit lonesome and vulnerable without any older relatives left.