How to overcome allergies
Constitutional weaknesses are often passed down from generation to generation. It sounds like your mother had a weakness in her lungs which manifested itself in asthma. The chalk may have just been a contributing factor, but plenty of school teachers have been around chalk dust, day in and day out, and have not developed asthma.
My guess is that your mother and father's constitutional weaknesses were embedded in the genetic make-up of her egg and his sperm, and were passed down to their children. You have a constitutional weakness that manifested itself in the sinuses and you likely passed that weakness on to your children.
It's good to know what your weaknesses are so you can be sure to avoid things that aggravate them. But in general, one of the best things you can do to overcome sensitivities and allergies is to boost the immune system.
In specific, I've found that people who have skin rashes or dry skin respond really well to increasing the essential fatty acids in the diet. This can be done by making sure the family is eating plenty of fatty fish each week. Some recommend 8 ounces a week. Good choices are salmon, tuna, oysters, pollock, shrimp, herring and sardines. Be sure to avoid fish that is high in mercury.
Other foods that are high in Omega 3 Fatty Acids are egg yolk, flax seeds or flax seed oil, walnuts, pecans, wheat germ and olive oil.
If you make a green smoothie each day for your children, and put some flax oil in it, it should greatly help your children's skin allergies. Here's a video showing how to make a super healthy green smoothie. The more sweet fruit you use (i.e. bananas, etc.) the less "green" you will taste. My children LOVE green smoothies and make them every day. You can start with less greens and work up to more later, but do start making some green smoothies and adding flax oil and I think you'll see some good change in your allergies.
It's also really important for anyone considering pregnancy to go on a preconception plan which includes a super healthy and clean diet, and a healthy lifestyle. It takes 3-4 months to create an egg which is mature and can be fertilized, and it takes 3-4 months to create healthy sperm which can penetrate an egg, so 3-4 months of preconception care (minimum) will be helpful.
Hope this information helps, and please post back with any questions you may have.