Active, Inactive textboxes

I have a form needs to be filled out. A lot of the questions are a yes/
no question. When they pick yes I want some other textboxes to be
active, and when they pick no I want the textboxes to be inactive.
Example - A question could be: Do you have siblings. If you check yes,
then other line would appear to say How many (other textboxes are
active)? If you say no, then it skips to the next question (other
textboxes are inactive - greyed out).
How do I do this? If it includes coding, can I get help with the
coding.