But what if my parents are atheists?

It does not matter how foolish or wicked a parent might be. They have an office and position of authority given by God, and they should be obeyed until they require you to disobey God in some matter. Even if in the rare event you must disobey them in a matter pertaining to God, you should still obey and honor them in all other matters. A rule to remember is that imperfect authority is better than no authority at all.

For further study of the Christian and authority:

Ordinance of Authority