I’m not sure that saving a few thousand NIS is a good reason for your brother to marry your sister-in-aw, unless of course, they had already decided to marry, even if you are Isamaelim. Friday weddings save money? Perhaps because there is much less demand to rent simcha halls erev shabbos and the caterer has lots of left over Chulent and other delites from Thursday evening along with other leftover food they are offering at a steal.
