"How is the relationship between you and your parents?"
many times the 的 will be left off if their is a close relation or relationship. For example you don't need to say 她是我的太太。(she is my wife). Though you can, but many times people will just drop the 的 in that situation. 她是我太太。
Really, that "的" before "父母" is totally not needed. The "的" placement isn't even the same for other sentences such as “我和我朋友的关系很好” , which doesn't have the "的" in front of the noun