Pronouns and declension for merged/hermaphroditic entities

Question

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.

Answer 1

Given that this type of entity is rare in our world, no pronouns of the type you seek have arisen. The phenomenon has not been of enough consequence to human history to warrant the development of such pronouns. As for those entities which do exist in such a form, we have little if any reason to emphasize the dual genders in the personal pronoun. We use "it" for non-human forms, and state the dual genders when it is important to direct someone's awareness to that point, rather than expect the pronoun to convey this information. In other words, we have no reason to go out of our way to devise a pronoun that points out the dual genders of a mated anglerfish pair. In those specialized, esoteric instances in which this entity is discussed, the writer would tend to say something like "the mated pair," or if choosing the pronoun, "it."

(In the case of human hermaphrodites, which are not the type of entity you describe, but which I mention for completeness, we use the pronoun that fits the individual's gender of choice.)

Contrast this with an imaginary world in a work of fantasy, in which the dominant creatures go through a crucial phase of development during which they form mated pairs of the kind you describe, and these mated pairs are essential to the survival of the race. In such a world, the kind of pronoun you seek would arise. This world, however, is not that one.