Their brethren? I believe you are uneducated if you are referring to the group I assume you are. Especially given the politics of the region and the differences/animosity between those groups
The fact that individual groups in the Islamist pond engage in constant hate and strife doesn't make them non-brethren. Ideological movements often engage in constant conflict over relatively minor differences. Obsession with purity is common in bigots.
Their important common denominator is "we believe in bringing about submission to Allah at the point of the gun". I would advise any "unbeliever" to stay the hell away from any such group.
That's the thing, that's not a common denominator if you really know what each group stands for and promotes. There are christians in Gaza under Hamas. There are different Muslim denominations in Gaza under Hamas. The other groups you are mentioning wouldn't allow this, they kill other Muslims for being different, and they attack christians. There is a huge contrast. What you call a common denominator is false. There are many "unbelievers" living fine in Gaza and in Palestine in general (ignoring that they are also being victims of Israeli attacks)
Islam, even in its fundamentalist form (Salafism, Wahhabism) doesn't call for outright extermination of "People of the Book", only their subjugation under the dhimmi status.
When Hamas lets Christians live, they are doing what Islam considers right. Outright pagans (polytheists) would be a different story.
Still, they enforce Islamic law where they rule. You cannot be openly gay, you cannot openly proclaim that you no longer believe in Allah (apostasy), a Christian man cannot marry a Muslim woman.
The fact that some other fundamentalists go further than Hamas doesn't make Hamas non-fundamentalists.
Their important common denominator is "we believe in bringing about submission to Allah at the point of the gun". I would advise any "unbeliever" to stay the hell away from any such group.