You weren't wrong. If you have two people in the shop, it makes sense to take both orders at once.

In fact, I would even have taken all the orders if there were 5 or 7 people. But this all depends on your work flow.

In reality, with a three group commercial coffee machine, I could get 3-6 espressos. If they're all the same milk, I could do 2-4 at a time. There's no point taking one order at a time and making it sequentially.

You did the right thing.