1) You must impress upon them that it is reported that the Prophet (sawa) said that if you find a potential spouse for your child who is a believer and has good ethics then marry them. Thus, these are the criteria that we must use. Try to convince them by explaining this, and that the inflallibles married women from all different places and cultures
2) There is no such thing as absolute duty to one’s parents, otherwise we would have to obey them in every matter, even sinful things (Allah forbid). Yes, we must respect and listen to them, however they are not allowed to rule over and decide a child’s life because every human being is free. It is true we cannot completely follow the perfect example of the Imams, but we must try, and at least live by its philosophy.