Normally, Checkboxes are designed for collecting multiple responses using a single question. Using Easy Peasy Forms, the checkboxes can freely be checked so hence you cannot limit the number of answers. However, you can provide instructions in each field of a Form, in which you can instruct a respondent to reply the way you want.
Another method is to use either Radio-Buttons (Option List) or List (Dropdown List). This can allow you to limit the number of answers from a respondent.