K.C.
You could do a Mexican dish like tacos, fajitas, quesadillas, etc. For any of these dishes, you'll need either tortillas or crunchy taco shells. Then you can add ground beef/steak/ground turkey, onion, bell pepper, cheese, guacamole, etc.
We do a lot of stir fry. We'll take beef and whatever veggies you like (mushroom, bell pepper, onion, carrots, broccoli, cauliflower, snap peas, water chestnuts, etc) and saute them with teriyaki sauce and garlic. Soy sauce works too. We generally serve it over rice, but your second child could easily just eat it by itself.
You could make pasta with a cream sauce, butter or garlic butter. You could add ground turkey to the sauce to add some protein.
You can make pizza with garlic butter instead of tomato sauce and then add cheese and any toppings you like.
For things like taco seasoning, gravy, and other seasoning mixes, there is a growing market of allergy friendly options. You'll need to start reading every label while you learn what does and doesn't work for your family, but it actually does get a lot easier as you go. My son is allergic to nuts, dairy, and eggs (though he's finally somewhat outgrowing the egg and tree nuts), so we've had about eight years of navigating the food allergy world.
If you have access to them, stores like Sprouts and Whole Foods offer a lot of allergy friendly options. Our local Ralph's (Kroger) carries a lot of it now too, and even Target is getting more.