orks & elves

[elven maiden Earwen]

i love hte books and i have been reading them for a while but im kinda comfused on something.

in on of the books i read that morgoth captured elves that wandered far to the north. he mutated them and they became what is known as orcs.but if that elf that became a orc had desendents wouldnt they be a kin to a orc and its desendents? do orcs have desendents? if they did and an elf killed the orc whom was a desendent of a elf and those two elves were related wouldnt that be considered kin slaying? help confused ~lalith