Substitute the nuts or leave out entirely

The coconut will no doubt work, as it's already in the recipe. But do you want that much coconut flavor?
You also just omit the pecans.
Last, you could replace them with (the same volume of) rolled oats or Grape Nuts cereal.
But the Grape Nuts has wheat, so if your guests have multiple allergies, that's out. Maybe, then, use a food like kasha (buckwheat) that behaves like a grain but isn't - it's related to sorrel & rhubarb.