Qi Sha Men has two factions. One the Life Faction where Ge Nie and Gao Jian Li are from. They get the fame and glory and power within the sect. The other is the Death Faction where Wei Zhuang, Xue Nv come from. They do all the assassination and dirty work to give the false impression that the dudes from the Life Faction are so powerful and unstoppable. So all who enter the Death Faction no longer have any self, life or identity, they are just like dispensable killing machines controlled by Ge Nie's dad, with no way out but by death.
Xue Nv and Wei Zhuang were sort of coerced into joining the Death Faction and thus have been given the death sentence, but upon the destruction of the Qi Sha Men, they got a new life where they could do what they want and have the freedom that they were deprived of when they were slaves.
Gao Jian Li and Ge Nie don't know about the Death Faction. So it is quite a blow to Gao Jian Li when he finds out since he thought that Qi Sha Men was so perfect.
I am not sure, but I think Jing Ke comes from another sect, most probably the Mozi, like DMR and co, where they preach universal love to end all wars.
Da Si Ming and Xiao Si Ming belong to the Xi Clan, headed by Dong Huang Tai Yi (aka eunuch Zhao Gao), which aim at toppling all kingdoms to take revenge on the Zhao kingdom which massacred their clan to take the blame for a military failure. Dong Huang Tai Yi and co were the ones who selected Tianming and implanted the evil curse into him, so that they could use him as their killing machine later on, probably to take on armies. But I think the power needs to grow and develop inside Tianming in due time so until Tianming comes under their control, Xiao Si Ming has to protect the valuable asset from harm.
I haven't watched the latest eps yet. Will change answer if anything different comes up.