I just discovered (yeah!) the Item Relations Plugin and would like to know if I can apply the FOAF to describe relationships between deceased individuals. Also, is there a way to augment the foaf:knows to include various family relationships? And if so, how would I go about it?
As always, thank you in advance for any help and insights you can lend on this topic.
Item Relations only pulls in the existing vocabularies to make them available. It sounds like you are asking about usage of terms from FOAF, which is really a matter of knowing FOAF usage, and is not Omeka.
That said, the FOAF spec linked to above doesn't seem to distinguish between the living and the dead (or, indeed, the undead, if your use case is that broad). From their spec about what a Person is:
We don't nitpic about whether they're alive, dead, real, or imaginary.In general, FOAF itself can be extended, but Item Relations won't know that -- again, that's outside of Omeka.