Its not a musical. I don't see anyone doing their research. Phillips a couple of days ago confirmed that it isn't. It's going to be similar as the first where music is an element to the story but it's not a musical.
Folie a deux translates as madness for two. According to IMDB Harley is a psychiatrist in this. Its not World Of Imagination! Its the beginning of What The World Needs Now. Gaga's voice suits Harley better than Margot as Harley is supposed to be from NYC but Margot used a Los Angeles accent.