All of your creatures will re-enter the battlefield at the same time. Your Lieutenant will see 4 humans entering, triggering the second ability 4 times. Because it also entered, its first ability will trigger once.
In other words, you don't have a choice in the matter, but you get your 5/5 Lieutenant anyway, and a +1/+1 counter on your other 4 humans.
No, they all enter at the same time, not one at a time. However, the Lieutenant will see the other Humans entering at the same time as itself and it will trigger for them. So you'll still get the triggers from the other Humans entering.
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DCI Level 2 Judge
Scientists have calculated that the chance of anything so patently absurd actually existing are millions to one. But magicians have calculated that million-to-one chances crop up nine times out of ten.