What is the proper nusach of zimun when kohen is present and the mezamin is non kohen?
What is the proper nusach of zimun if the baal habyis is kohen and mezamin is not?
If the person is a guest that is leading the zimun, he should say “b’rshus baal habayis, kohen, moronon v’rabonon etc…”. The reason for this is that the person leading the zimun should take permission from the baal habayis, and also give honor to the kohen. (It is preferable to mention the baal habayis before the kohen, because the baal habayis is the one to give out the honor of leading the zimun, and if he wants, he may lead the zimun himself, without giving it to the kohen. Therefore he is mentioned first.)
When the baal habayis is the one leading the zimun he can say it the regular way, because he does not need the cohen’s permission, however it is preferable that he say b’rishush kohen, because it is a mitzva to honor the kohen.
M:B 167- 75, Shar Hatzion ibid, Horav Y. Cahen shlit”a.