The old bay goes in the water, not on the shrimp?
Odd.
Ideally you'd put shrimp-and-crab-boil in the water but you likely don't own any. Regardless extra Old Bay should be provided at the table. For dippin'.
You know you could serve them something actually vegetarian, too. Just a thought. This is my favorite vegetarian dinner, though you'd likely need to at least triple it:
Lemony Chickpea Stir-fry
2 Tbs ghee or olive oil
1 sm onion or a couple shallots, sliced
1 Tbs garlic, minced
1 can chickpeas, drained & rinsed
1 cup baby spinach or chopped hearty green
1 red pepper, roasted, skinned, and chopped
2 small zucchini, cut into semi-circles
zest and juice of half a lemon
Heat 1 T oil over medium-high heat. Add a pinch of salt and the chickpeas. Saute until beginning to color. Add onion and garlic and continue to cook until the chickpeas are deep gold and the onion is translucent. And greens and cook until wilted. Evacuate everything to a plate.
In the same pan heat remaining oil over medium heat and saute the zucchini until lightly browned. Add the pepper and stir for about a minute. Return chickpea mixture to the pan and stir to combine. Remove from heat and add the juice, zest, and pepper to taste.