where did you get the filing under the mother's name from - the IGI adopts the English (not the usual Manx) custom of putting illegitimate births under mother's name - Manx custom had been to use father's name where this was acknowledged (or claimed by woman) - births were legitimised if couple married within 2 years - however as 19th C progressed Manx law became more like English law and in your case with several children involved sounds somewhat difficult.