gender - Pronouns and declension for merged/hermaphroditic entities

I have a pair of friends who since entering into a relationship have become rather disgustingly effusive and clingy, to the point where people around them have begun referring them an 'it' [singular], or as a (hermaphroditic) single organism. Equivalently, imagine attempting to speak to a sentient coral, or a Portuguese Man o' War, or a mated anglerfish pair, wherein

When [the male] finds a female, he bites into her skin, and releases an enzyme that digests the skin of his mouth and her body, fusing the pair down to the blood-vessel level. The male becomes dependent on the female host for survival, receiving nutrients via their shared circulatory system, and provides sperm to the female in return. (Wikipedia)

My question is, is there an accepted or even simply precedented way to correctly refer to an entity of this nature? 'It,' for example, is passible, but it's really a neuter pronoun, rather than bigendered. Similarly, trying to convey the two-in-one-ness is difficult, especially when attempting to decline it in a sentence:

Which of it was here yesterday?

('Which part' is again, passable, but to me seems to imply inanimate parts of a single organism, not sentient parts of a merged one)

It fucked itself.

I feel that the singular, genderless 'they' might be useful, but apart from being questionably grammatical, definitely implies a separation.

Perhaps useful; how is the Holy Trinity referred to in scholarly texts?

Edit: To my dismay, a number of people seem to have taken this question as insulting, or 'ask[ing] how to insult people whose behavior you cannot tolerate,' or 'look[ing] at the phenomenon in a perverted way.' None of these interpretations are accurate. Rather, I was amused by the concept, which was not coined by me, and wondered upon the possible grammatical constructs. Believe me, I can insult people quite well unassisted.