When Raziel was one of Kain's vampire lieutenants, he, like all the others, had a clan. They were his vampiric descendants. Following the naming conventions in Soul Reaver, it can be assumed they were called the 'Razielim' (or perhaps the 'Razelim' as the 'i' of 'Melchiah' was dropped for his clan's name: the Melchahim). The Razielim territory was to the west of the Abyss, next to Melchiah's lands.
In Soul Reaver, Raziel was condemned to the Abyss upon presenting his newly-grown wings to Kain. However, Raziel wasn't the only one to suffer for his transgression. Following his execution, the Razielim clan disappeared from Nosgoth. Presumably they were all hunted down and killed according to Kain's orders. When he returned from the Abyss, Raziel certainly believed that to be the case.
As a Reaver of Souls, Raziel revisited his former stronghold. He was mildly shocked to find it desolate - his "once proud kin, wiped from this world like excrement from a boot". He immediately held Kain responsible, and he questioned Melchiah about the fate of the Razielim during their encounter. Later, in the Sanctuary of the Clans, he expressed his outrage to Kain himself. Angrily, Raziel said that the genocide of his clan was "unconscionable". Kain was unremorseful, and retorted that Raziel was not in a position to question his judgement about the matter. What Kain had made, he could also destroy.
There has been some speculation amongst Legacy of Kain fans that the Razielim may have in fact survived, in some form or another. If they did, it is assumed that they would have followed Raziel's evolutionary path, eventually growing bat-like wings like his. All of the clans in Soul Reaver evolved in a similar manner to their lieutenant-patriarch.