Problem 1 - Hmm...can't help on being nice - it's not my strong suit. Is it really that hard though to do a Primal-ish dinner though? I feel like I may be spoiled, but my in-laws mostly cook Southern style, so dinner is typically some meat, some greens, and biscuits that I can just skip. The worst stuff I eat over there is fried fish and the occasional pie filling. My parents are a bit trickier because Mom's a vegetarian and they keep kosher, but she makes me awesome salads and egg dishes, and doesn't mind if I cook fish for extra protein. Of course, this is all a moot point if your in-laws are just being jerks about it.
Problem 2 - The incredible edible (hard-boiled) egg! Seriously - my favorite snack. I keep seasoning salt in my desk at work. I make them by the dozen and keep them in the fridge, and bring them with me when I don't have time for breakfast. I also like cut up apples with almond butter (not the best for weight loss, but fine for kids), cut up veggies with dip, canned sardines, and cold sausages. I pack lunch for work most days - either a big ass salad, leftovers from dinner, or chili con carne.
Problem 3 - Yes, you can eat meatloaf for every dinner, but someone will probably start refusing to eat it very soon

Though I do currently have my husband eating chili for 4 meals a week or so. So...what about chili? It's fast, it's cheap, and most people like it. Let me know if you need a recipe. In general, what types of food do you and your family like?