I need to cook 3 9x13 dishes and a pie shell....can I cook all4 in the oven at the same time?

Hi there! You should be able to, as long as you can fit some space between the dishes to allow for air flow. You will also want to rotate them and you may need to adjust cooking times and temperatures for each dish. Plus make sure to check on each of them frequently for doneness! Here are some additional tips on cooking more than one dish in the oven at once:
https://food52.com/blog/7719-where-to-put-the-oven-racks-alice-s-rules
https://food52.com/hotline/38422-baking-multiple-pies-at-once

What will be in your dishes? What temperature would you be using? If it's at all possible you could bake the pie shell the night before.