"No matter how big or how small, there were as many cultivational sects as stars in a night sky." ― Narration[source]Cultivational sects (玄门世家, Xuánmén shìjiā) form the major community of cultivators in the world of Grandmaster of Demonic Cultivation.
In most cultivation novels, cultivation is carried out in sects or schools (门派) where people pay their respects to a master in the hopes of being taken in as a disciple.
GDC takes a different approach: cultivators in here are organised mainly by clan or extended families (姓氏), usually related by blood to the founder. This follows the same lines of ancient Chinese nobility, and thus highlights the importance of relationships (关系) in the world of GDC.
Lan Qiren taught that the first cultivator to focus on his clan rather than the sect of cultivation was Wen Mao, who would later found the Qishan Wen Sect. Back then, with the lead of Wen Mao, the cultivation world focused on the rise of clans instead of sects, and cultivational forces connected by blood ties rose as if they were bamboo shoots after a spring rain. Without exception, every cultivator who was slightly famous chose to found a sect. Lan An would later follow this trend in some fashion to found the Gusu Lan Sect.
Of the remaining survivors from this generation, there is only Baoshan-Sanren, who chose to seclude herself away to maintain a secret school of pupils.
The most prominent clans were:
In Wei Wuxian's youth, the Qishan Wen Sect's tyranny stretched the patience of other clans to its limits and the Sunshot Campaign to destroy the Wen clan began, and ended with the sacking of Nightless City.
Chief Cultivator (仙督)
In the wake of the Sunshot Campaign ending, Jin Guangshan sought to follow the Wen clan's rise in power and become the Chief Cultivator, the nominal leader of the cultivational world. When the Lanling Jin Sect was about to succeed in this endeavour, though, Jin Guangshan died of a stroke (allegedly mid-orgy).
All of the cultivation sects were skilled in different areas. Similar to how the GusuLan Sect was skilled at music, the violence and power of the QingheNie Sect’s saber spirits were how it outshone the other sects. 
Each cultivational sect tends to follow the path and basis of cultivation determined by the founder. For example, the Gusu Lan Sect's expertise in magical music comes from Lan An's occupation as a musician; the Qinghe Nie Sect's expertise in the saber comes from their founder's occupation as a butcher. If it abandoned its founder’s ideal and started anew in search of a different path, who knew how many years it’d take, or if it’d even succeed or not. From the founder thus also comes the sect's uniform, motifs, habits, and lifestyle tendencies.
This creates a complex situation when problems arise in the descendants' cultivation. For example, the Qinghe Nie Sect's current leader Nie Huaisang faces the risk of dying young like his elder brother Nie Mingjue of a qi deviation. He cannot sharpen his cultivation, else he would die; yet, it is his current weakness as leader of the Nie sect which leads to the Nie clan nearly dropping from prominence since the time of Nie Mingjue.
The cultivational sects on a whole seems to observe the Dishu system of inheritance. Undercurrents of worrying over the inheritance of the clan leadership exists throughout the four major Cultivational Sects.
The Gusu Lan Sect is possibly the least problematic sect in terms of passing down the clan leadership: Qingheng-jun had only one main wife who bore two sons: Lan Xichen and Lan Wangji. The oldest son, Lan Xichen thus took over the clan leadership. Despite falling out with most of his clan over his choice of wife, Qingheng-jun's marriage was still recorded in the clan records, and thus all children begotten from their union were, in the eyes of Chinese law, legitimate inheritors. Despite the brothers' uncle Lan Qiren (himself also presumably a direct legitimate descendant of the clan founder) having seniority over them, the leader of the Gusu Lan Sect is Lan Xichen due to the Chinese rule of inheritance.
The legitimacy of sons is even more pronounced in the case of the Lanling Jin Sect: Jin Guangshan has only one main wife and one legitimate son Jin Zixuan, but has several illegitimate children outside of Lanling. When Jin Guangyao became legitimised, there was still minimal issue even as he began to rival Jin Zixuan, because it seemed as though Jin Guangyao could not legitimately become clan leader. After Jin Zixuan's accidental death, though, the clan leadership would have directly fallen to Jin Ling, who by then is the only legitimate grandson of Jin Guangshan. Jin Guangyao took over as clan leader, yet it is important to remember that Jin Ling has higher priority of inheritance over his uncle.
The Yunmeng Jiang Sect faces a different problem; there was never any question that Jiang Cheng would be the next clan leader. However, with Wei Wuxian outshining Jiang Cheng and Jiang Fengmian's preference for his eldest disciple (Wei Wuxian) over his own son, plus rumours of Jiang Fengmian's former courtship of Wei Wuxian's mother Zangse-Sanren, Yu Ziyuan possibly began to oppress Wei Wuxian and push her son to work harder to outshine his fellow disciple.