Where did I say that one should serve kitniyot to Askhenazim? Or that Askhenazim should cook kitniyot for themselves? Obviously the Askhenazi is taking the bother to check the rice in order to feed their favourite (and permissible to them) dishes to his Sefaradi family and friends.
What I said is completely different, i.e. if someone cooks rice and beans in a pot, and he can do that regardless of being Askhenazi or Sefaradi (no restriction on Askhenazim owning and benefitting from kitniyot), and immediately afterwards cooks potatoes in the same pot, those potatoes are fit to be eaten by Askhenazim, and this is the case even if the pot was not even washed with detergent, in fact, even if a few grains remained attached to it. Thus, observant Askhenazim have no problem at all eating in a home where observant Sefaradim cook and eat their kitniyot. Of course, as long as there is no chometz.