...English-speaking people can pronounce these three variants the same! I'm not sure about how to pronounce
Madeleine in English, I only know the proper French pronounciation.
I would pronounce
Madeline Mad-uh-leen, like
Emmeline and so on, but I guess that's not common. Mad-uh-line also makes sense (more sense than Mad-uh-lyn, imo).
Madelyn is mad-uh-lyn to me, too.