The night Hanako and Tsukasa died...

What happened the night of the Yugi family tragedy? The event that created the "Redhouse?" What are your theories? Did Tsukasa abuse Hanako? Did he do it for the brother who disappeared the night of their 4th birthday? Did the "demon" Tsukasa love Amane? What happened to the one that Kou and Nene met at the Red House?