Are you saying you have to Edit Family of the Sheet in order to change the number? That sounds like you've just put a Text item onto the Sheet. And of course, when you edit the Sheet family and change that Text field, it's going to reflect on every sheet you have in the project that is of that sheet family.
What you need instead is to Create > Label in the Sheet and assign that Label to the existing Sheet Number parameter. Then updates to that parameter happen within the project and are unique to each instance of many sheets you have.