A pair of Williamsburg moms and business owners have launched a progressive new Shabbat service with the help of an unlikely benefactor — The Roman Catholic Church!  Leah Fink and Allyson Stone launched their new Shabbat service, called B’nai Brooklyn, at Our Lady of Mount Carmel on Havemeyer Street on Nov. 15, and the collaboration between faiths has since blossomed into a thriving religious community, according to Fink.  “We were blown away by the reaction,” said Fink, an educational consultant and owner of ClassesAt. The women created B’nai Brooklyn to address the need for a more progressive Reform Jewish synagogue amid the area’s large Orthodox community, but they struggled to find a venue until Fink’s father, Danny, suggested …