How are those who claim there is no need for scholars to understand the Qur’an and Sunnah, and who interpret the Qur’an and research hadith themselves, to be dealt with?

Acquiring knowledge is done by receiving it from scholars, not initially from books, because knowledge is a craft that requires a teacher. Whoever enters into knowledge alone leaves alone.

If a شيخ (scholar/teacher) is not available, one can acquire knowledge from reliable books and websites, and from those who are recognized for their knowledge and piety. Among the reliable Tafasir (explanations of the Quran) are: Tafsir Ibn Kathir, Adwa' al-Bayan by Al-Shanqiti, Tafsir al-Sa'di, Al-Tafsir al-Wasit, Al-Tafsir al-Muyassar, Mukhtasar al-Tafsir, and other Tafasir that are characterized by a sound methodology.

It is also possible to listen to the lessons of trustworthy scholars through available recordings online.