Hello frost0. Regarding your questions:
frost0: - Blood Omen: Legacy of Kain
Good question. Square Enix seem to own the Playstation 1 version, which is why they have been able to rerelease the game on PSN. As for the PC version, it's probably Activision, though there have been comments that things aren't so straightforward and the righs might actually be split among multiple parties.
frost0: - Call of Cthulhu: Dark Corners of the Earth
It's owned by Bethesda. They publish the game on Steam and other official Steam key resellers (GamersGate, GreenManGaming, Humble Store).
The developer of the game, Doug TenNapel, mentioned that EA hold the rights to the game, but despite all efforts to contact them for a possible rerelease, there has been no success so far.
frost0: - Blade of Darkness
Another good question. The game was originally brought here by Codemasters in 2013, only to be removed one year later, because Codemasters lost the publishing rights to it. No idea who is the current owner.