No need to give them yogurt, but if you want to, you could give them an avian specific probiotic. Some like to give cat food to boost protein levels (peafowl people do this), but there is no need to. All they really need is fresh lay pellet or crumble and free choice oyster shell. I also give mine table scraps as long as there aren't any foods that are toxic to birds in it. The majority of their food should be a poultry feed, period.
-Kathy
x2 Well said.