Looking at the 5e MM, I'm not sure how many non-hostile creatures are affected by the Hobgoblin Captain's Leadership action - only one, or all of them within 30'?
There is no limit to the number of creatures that can be affected
The Leadership action states the effect can be activated:
whenever a nonhostile creature that it can see within 30 feet of it makes an attack roll or a saving throw.
There is no limit to the number of times this can be activated during the 1-minute duration. It can be used on 1 creature, 100 creatures, the same creature 100 times.
The only restrictions are that they are within 30 feet, can hear and understand the captain, are not already benefiting from leadership (eg if there are two Hobgoblin Captains at the same time, they can't both buff the same roll), and the captain isn't incapacitated.