One of my nephews went to each set of parents to discuss it. He did not "ask permission", instead he approached it by asking the parents what they thought about it if they did get married; did they have any concerns or issues to discuss before the two of them officially became engaged. His objective was to keep things as harmonious as possible between the parents and to address any concerns they may have in an upfront manner. I have to say, so far it's worked. Both families get along well, spend time with each other, and there are no arguments or jealousies regarding holidays or who's house they are spending more time at.