Watching Alexander Lightwood Mikaelson- WTS Crossover

What if Alexander Lightwood was never Robert's Son but instead Klaus Mikaelson & Maryse Lightwood Son? And how would this change things? And what would happen when The Full Shadowhunter's Cast was teleported into a movie theater to watch Alexander Lightwood Mikaelson? How would the Lightwood family react to finding out they have another family member they didn't know they had? And what will happen when they find out he is a Mikaelson & the soulmate to Magnus Bane? And how would Magnus feel about being mated to a Lightwood & a Mikaelson?
Alexander Henrik-Kol Lightwood Mikaelson X Magnus Bane