Is it permissible for a husband to feed his wife in front of his parents and unmarried sisters, and are there examples of this from the Prophet's Sunnah or the lives of the Companions and their successors?

There is no religious impediment for a husband to feed his wife in front of her family, provided that provocative behavior and immodesty are avoided, and the prevailing custom is observed if it deems such an act contrary to chivalry.