I am not a chef, but i will try to give you some pointers and directions to look in.

First of all, just get an oven bag (plastic thing, sold in boxes at all stores) follow the instructions. Bake just the turkey. make stuffing in a different dish. The bag keeps all the moisture in the Turkey, and it comes out just right.

Now, how did your grandmother do it?
Mostly basting.

First your rub the skin with oil. This not only browns the skin, to make it look good in pictures, but also makes the skin a protective shell keeping all the moisture in. Basting the turkey a few times during baking is like repeated applications of oil, turkey oil.

Basting does not get into the turkey, the skin blocks liquids from getting in. So, it is all about keeping the steam inside from escaping.

The aluminum foil is a direct heat shield. It keeps the IR from hitting the bird. This is to save the skin from becoming blackened. The air temperature in the oven is what actually cooks the insides. The aluminum foil is important in backing pies, because the edges of the crust can become over cooked (blackened) and the aluminum foil keeps the IR from doing it in.

Then there is the brining. (Brine - salt water and spices) you soak the bird in before baking. Many supermarket turkeys are pre-brined. Look it up if you are interested.