Can multiple slabs of ribs be baked at once?
If the oven is large enough, you can bake as many slabs as will comfortably fit on one tray or oven rack without any adjustments.

If you need to seriously cut the total baking time, you could use even two trays at the same time, but in this case, you need to make sure the ribs get enough heat from all sides, which means swapping trays and turning the ribs occasionally and probably baking for a bit longer - I'd guess fifteen to thirty minutes - to compensate for the less-than-ideal heat exposure. I'd leave the temperature setting unchanged unless you notice excess or too little browning halfway to the parbaking. 



Not part of your question, but probably worth mentioning, as I assume you will be serving the ribs to many people:

Whatever method you finally choose, note that such a large amount of ribs that will be ready for further processing will need some extra actions to ensure all the meat stays safe and not in the danger zone for more than two hours. So you might want to think about either keeping your meat hot (above 140F/60C) or cooling it down quickly (below 40F / 4C). Find more details and useful links in our canonical post.