If you tell them about the allergies they will provide you with a special menu of the foods that can be made safely (for multiple allergens my guess is that they will provide two or more special menus, and you will have to cross-reference, but I'm not sure, we only have seen the PN/TN allergy menu). They will prepare the allergy-safe dishes in a separate part of the kitchen, with separate pans & utensils, and use new packages of ingredients. At least this is what ours told us they do, and they were very good with us (our first time we had a TNA waitress). I suggest you call ahead to make sure that this is what they do at your local one. I also suggest making reservations.
And I must say--their food is delicious!