This is what I'm thinking too now. I don't remember what he said about his mother in the past... but is there any chance his mom worked there and she's the one who actually died? Now the dad is pissed, went off the grid and has this big plot for revenge with his kids? I really don't remember how he said his mom died though.
Did Angela ever say specifically that Elliot's dad died there or did she just refer to it as "our parents died"? Now I want to go rewatch things. This show is great. Haha. I'm still staying on team real for Mr. Robot. But I think when Elliot thinks of his mom who was abusive towards him, it was really his dad. Hence the pushing him off the ledge and whatnot. I think he was probably a fine dad until the mom died, explains the nice photos. Then he got weird after his wife passed away, which supposedly the mom did according to Elliot. But I'll say the mom is the one who died, he's just not remembering it correctly because he's obviously messed up in the head.
Or maybe I'm just trying to think of ways for Mr. Robot to be real. lol