We have been invited to a family simcha where the seudah is not under supervision and is at a traife (expensive) hotel, but we have been offered a kosher supervised meal. Should we attend as we do not approve of serving a traife (albeit fish/veg) meal at a Jewish and religious function? My family has said they would be very upset if we don’t come as we are only a small family. It is not a case of money that they are having an unsupervised function.

Family relations are a two-way street. Your family would be upset if you don't come. You should explain to them that watching your family, about whom you care deeply, eating treifot (lobsters and shrimp are as not- kosher as bacon) would make you so unhappy that the spirit of wedding simcha would be totally absent. Suggest a smorgasbord in the shul after the chuppa where you could dance and sing with the couple, but explain that your spirit at a non-kosher meal would be one of sadness. Alternately, make sure that they have a vegetarian meal that has no real treifot in it. You of course could not eat without a hashgacha but you should participate if the affair is only vegetables and macaroni etc.