With the roasts and the pudding, your ovens will be getting quite a workout. Forgot the roasted vegetables and make something you can do entirely on the stove top. Creamed spinach is an excellent choice -- it will not only go quite well with the potatoes and the roast, but you can make it the day before. A day in the refrigerator and a long, slow reheat only make it better.
It depends, of course, on which cut of beef you're planning to roast, but it's likely you'll be doing two roasts. For roasts without a bone, plan on about 3/4 pound per person of raw weight for the average group. For standing rib roasts (bone in) allow one bone for every two people. Two six bone roasts (those are full "prime ribs") is exactly right for your group size.
A very easy "au jus" can be made by mixing two or three parts beef stock (boxed or canned is OK) with one part red wine. Bring to a hard boil, then reduce to a simmer and cook until the "winey" taste is gone. About 15 minutes.
I hope you're making a horseradish sauce to go along with the beef.
It will make your life easier if you have a large foam or fiberglass drinks cooler handy. When the roasts are done (use a meat thermometer and cook them 5* - 10*F lower than you want to serve) wrap them tightly in aluminum foil, put them in the cooler, and stuff the extra space with crumbled newspapers, blankets or wadded up towels. Then close the cooler tightly. For the first ten minutes or so the internal temperature of the roast will creep up to exactly where you want it; then stop and hold. The roasts can rest in there for as long as three hours and stay hot without overcooking. An hour in the cooler will make for a roast that is easy to slice, and very juicy.
Even a well-rested roast will express some juice when it's carved. Have a wood board with a channel for carving.
One of the benefits of resting the roast this way, is that you've got the full use of your oven. Roasts like to finish in a medium-slow or medium oven, while Yorkshire pudding prefer hot. Don't forget to preheat your muffin tins -- or whatever it is you're using for the puds -- before you fill them. You want them smoking hot. For a super-delicious pud, use a mix of melted butter and renderings from the roast as the fat base.
The variety in your dinner menu is sufficient unless some of your guests have dietary restrictions. If you are going to add another protein course, do a fish not a poultry and keep it as basic as possible -- poached halibut for instance. Your menu so far is good ingredients, simply prepared -- that's a good thing.
I'm sure your party will be great and the outlaws duly impressed,