There's no limit to the amount of Fire Sticks you can have in one house or on one account although you're limited to using two Fire Sticks at one time for streaming with Amazon Prime and Hulu and Netflix limits you to streaming from one Fire Stick per account.
But you can have as many Fire Sticks you want too on one account and in your house, you're just limited to how many you can use to stream movies and shows from at one time.