English Translation
The woman sitting across the street is his current wife.
“…who is sitting there opposite…” would it be an expression?
As a native English speaker who is not a native Hebrew speaker, but basing my response on Hebrew-English sentence pairs containing “ממול” that I see at Reverso Context, I think it’s possible, but we’d be more likely to say “opposite him”, “opposite from him”, or “across from him”. I think “ממול” means “opposite” or “across” without specifying what is in between, which here could be “the table” or “the street” or something else.