Nightmares... about my dad?

You're having nightmares because you're putting too much pressure on yourself. You've been the "connection", but you don't have to be it any longer. There comes a time when things must be let go. If your brother and sister ever want to connect with your dad, it won't be, and shouldn't be, through you. They are adults. They can carry their own burden. Secondly, you're older now, and have more going on in your life. Six weeks is way too long for someone with a social life. One week, two weeks max. They'll understand. People grow, grow up, and outgrow.