Are the Qur'an and Hadiths both holy books in Islam?

In a sense, yes. They both are important texts to Muslims, however the Qur'an is the text that is of highest importance. Muslims believe that the Qur'an is the direct word from Allah revealed to them through the Prophet Muhammed, and that it is still the original text - that is, it has remained unchanged since its revelation. That's why Muslims, even when their first language isn't Arabic, try to learn to read the Qur'an in Arabic so that the word of Allah doesn't get changed in translation. Because it contains the word of Allah, it is arguably the most important text in Islam.
That being said, the Hadiths are also treasured by Muslims. The Hadiths doesn't contain the word of Allah, but it is instead more of a guidance text written by the Prophet Muhammed. He is believed by Muslims to be the ideal human, and they all strive to be like Allah's prophet. The Hadiths wasn't written by Muhammad but was compiled after his death by those closest to him, and it contains all his guidance, advice and sayings. It is used often by Muslims in every day life and also in Islamic law to help with decision making and as a source of answers for common problems. It is not necessarily a holy book in the same was as the Qur'an is, but it still holds a very special place in Islam.