Setting a minimum and maximum for checkboxes (limit, limits)

First edit your checkbox element.

1. Select the "Advanced" section
2. Define the "Max characters/selections allowed" and set it to 2, to limit the possible checkbox item selection to two.
3. Optionally define a minimum, if you want to make the checkbox a required field

Now click "Update Element" to save your changes.

Now when a user fills out the form they are required to choose at least 1 option and a maximum of 2.