Yatzmich
“and for sure once their engaged (Hashem has done his work) everybody else should stay out of it.”
Sorry but in Judaism the engagement is nothing. There is no Halachic Inyan that takes place and there’s no reason not to break it off if new information comes to light that wasn’t known or was hidden before. Your example from the Chazon ish has nothing to do with the case at hand where the actual boy has serious religious problems (not his siblings!)