Who must be killed to defeat ISIS and Al Qaeda?

Wrong question. Wrong approach.

You can't defeat these organizations by "killing" members. You defeat them by destroying the ideology & philosophies that makes them worth joining.

Sadly, we need to kill all of them to get rid of the cancers that these two groups are

CPT (Join to see) I think we need to continue knocking off the snake's head, because it does slow down their momentum momentarily, but that is not what will win this war. This war has to be won by converting this radical form of Islam back to the true peaceful religious beginnings and understandings of Islam:

Islam: is a monotheistic, Abrahamic religion articulated by the Qur'an, a religious text considered by its adherents to be the verbatim word of God (Allāh), and, for the vast majority of adherents, by the teachings and normative example (called the sunnah, composed of accounts called hadith) of Muhammad (c. 570–8 June 632 CE), considered by most of them to be the last prophet of God. An adherent of Islam is called a Muslim (sometimes spelled "Moslem"). ‪

Muslims believe that God is one and incomparable‪ and that the purpose of existence is to worship God. Muslims also believe that Islam is the complete and universal version of a primordial faith that was revealed many times before through prophets including Adam, Noah, Abraham, Moses, and Jesus. They maintain that the previous messages and revelations have been partially misinterpreted or altered over time, but consider the Arabic Qur'an to be both the unaltered and the final revelation of God. Religious concepts and practices include the five pillars of Islam, which are basic concepts and obligatory acts of worship, and following Islamic law, which touches on virtually every aspect of life and society, providing guidance on multifarious topics from banking and welfare, to family life and the environment. ‪

Jihad means: "to strive or struggle" (in the way of God). Jihad, in its broadest sense, is "exerting one's utmost power, efforts, endeavors, or ability in contending with an object of disapprobation". Depending on the object being a visible enemy, the Devil, and aspects of one's own self (such as sinful desires), different categories of jihad are defined. Jihad, when used without any qualifier, is understood in its military aspect. Jihad also refers to one's striving to attain religious and moral perfection. Some Muslim authorities, especially among the Shi'a and Sufis, distinguish between the "greater jihad", which pertains to spiritual self-perfection, and the "lesser jihad", defined as warfare.

Within Islamic jurisprudence, jihad is usually taken to mean military exertion against non-believer/non-Muslim/Muslim combatants who insulted Islam. The ultimate purpose of military jihad is debated, both within the Islamic community and without. Jihad is the only form of warfare permissible in Islamic law and may be declared against illegal works, terrorists, criminal groups, rebels, apostates, and leaders or states who oppress Muslims. Most Muslims today interpret Jihad as only a defensive form of warfare. Jihad only becomes an individual duty for those vested with authority. For the rest of the populace, this happens only in the case of a general mobilization. For most Twelver Shias, offensive jihad can only be declared by a divinely appointed leader of the Muslim community, and as such is suspended since Muhammad al-Mahdi's‪ occultation in 868 AD.

Somehow we have to convince the Islamic population throughout the world that their religious beliefs are theirs and we should acknowledge that belief. Somewhere down the line we (Infidels - a person who does not believe in religion or who adheres to a religion other than one's own) isn’t the enemy. One religion should not try to convert or cleanse the other.

Maybe someone out in RP land understands it better than me, but this is where the problem needs to be solved (at the root). All religions should be able to live on this earth and practice those religions and not persecute the others that don't follow their religion.

I probably have this all wrong or is doesn’t make sense, but it does to me. Find the root cause and work to change it – short answer!