We've been non-dairy for a while now and you're right, I've struggled to find good ways to make creamy non-dairy sauces for a while. Here's what I've found works well if wanting to substitute soy milk for a can of evaporated milk. You will need a good blender. Add 1/3 cup raw cashews and 1 cup of soy milk to your blender, a tsp of chicken seasoning helps disguise the flavor of the milk. Blend for at least 2 minuets, check to be sure all the little cashew pieces are smooth. Add to your recipe. This is something you can vary and mix up with different flavors as well, but is nice and creamy due to the fat in the cashews. A little roasted red pepper (you can buy it in jars) and some sesame tahini (pureed sesame seeds, kind of like a peanut butter, comes in a jar - look in the international section of your grocery store) will give your milk a cheesy flavor, good for potato or broccoli soups! I like the flavor of this cheesy stuff compared to soy cheeses that do melt, but don't taste as flavorful!
I'll pass along my recipe blog to you as well. We're vegetarian, but I use a lot of substitute meat products, so you could just substitute the real deal back into the recipe (since I often go the other way). I have a good recipe for gluten chops, these work well to substitute for your son instead of beef. They're easy to make and full of protein. martasrecipes.blogspot.com You'll see categories on the side, there are pages and pages of recipes to choose from.
Another thing, there are great soymeat products in the freezer section of the grocery store, things like burgers, crumbled hamburger to add to sloppy joes, chili, spaghetti sauce etc... Sausage links, chicken patties, nuggets... Look by the breakfast foods (eggo waffles and OJ).
Best wishes, this is tough, but you'll figure it out!