Act 1 encompasses everything before you first step into the manor. Act 2 starts there and ends at the church if im remembering right. Then Act 3 goes up till current content. I think one of the update blogs can help with Lyx, im pretty sure i gad to look at it several times to figure out what to do.
Edit: found it. Lyx will appear in Act 3 after you have met Claire in Act 3 and gone to sleep. The event should trigger then, and Lyx becomes available to talk to in the Manor's West Wing