My mother-in-law had 3 children. The first one, a boy, was born through a cesarian. The second one, a girl, was also born through cesarian and my husband, the third child is the only one born in the normal way. For some unknown reason, they made Pidyon Haben on the first son... is it right? If not, should anything be done now to retify the situation?

The Sulchan Aruch YD 305 writes that when born via Caesarean no Pidyon is done, nor for other brothers born later, normally. Rabbi Yitzchak Grinblat