No that rule only follows with feminine nouns that end with ई, लड़की = लड़कियाँ. But if a masculine noun ends with anything other than आ, like here with आदमी, also सेब​, पलंग​, दिन​, etc. then there is no change, the plural is the same word as the singular.

When you are talking about multiple people or things you use हैं, the only time you use हाे is when you are talking to someone, तुम हो or आप हो, but talking about other people will be either है or हैं depending on plurality.