Threadwielders (a/k/a Threadweavers) are a mostly acorporeal, quasi-immortal species that are technically immigrants to the universe from a different one - while simultaneously being the makers of the universe as a whole. They have a mostly tacit understanding of how the whole thing works - and how to tweak it so it does something else.
Biology
Threadwielders are chiefly invisibly encoded as information into the universe when they move through it. Much like a fungus and its fruiting body, Threadwielders are much larger entities than their avatars might suggest, and the more they age, the more 'space' they take up. Threadwielders do need their avatars to interact with the world. Each avatar has an acorporeal component (the one that can hypothetically manipulate Thread) and a corporeal one, and the corporeal one does not have to be visible at all. The corporeal part is a bit like a thin layer of skin - it can be prised off and a new one sought, but that's a dead-end without any Thread to graft itself to the new 'skin', and incredibly difficult without at least an alibi corporeal avatar to stay in touch with physical reality, since without perception of it, it's like swimming blindly in a zero-g ocean trying to find the surface to break through.
To kill a Threadwielder, one would have to trap its corporeal avatar, poison its acorporeal avatar to prevent it from detaching from it, use its structure to find the informational component, and rewrite (scramble) enough of it to turn the Threadwielder little more than random cosmic background noise - certainly nothing sapient. (This is exactly what Teranyina does.)
A complete destruction of a Threadwielder's avatar is 'survivable' for the Threadwielder, in that nothing threatens the informational component. The creature can even resurrect out of that particular torpor, as long as other Threadwielders are so kind to create them a new avatar.
In the most abstract sort of sense, they reproduce sexually; it's something that happens between acorporeal avatars, though mediated through the physical world, which is to say, corporeal avatars have to have some proximity to each other (or the aformentioned 'blind swimming' causes a chance encounter, but that's of course not practical). Nonetheless, they're genderless - there are no roles in such an encounter. There's also no social component to the interaction, other than the resulting responsibility to care for the offspring, so in practise it's used exclusively for procreation - though it could hypothetically be used as a rather effective form of blackmail, since no consent is actually necessary, but responsibility is assumed anyway.
(It's quite independent of what corporeal avatars do, too. Two Threadwielders could take a liking to sex as we humans understand it and nothing would come of it. As such, it's theoretically possible to have 'sexual' Threadwielder interaction with strong social components - one that exists between corporeal avatars. It would just have nothing to do with their actual reproduction.)
Culture
The attitude of Threadwielders tends to be fairly meh for a culture of de-facto deities. They have no rules about what's ethical to do to their pet universe, short of respecting their kin and accountability for one's actions. The lack of strong societal values, however, is in part what makes them good Guardians of other sapient species: They can adopt their pet culture's values almost entirely.
Actively causing the death of another Threadwielder is immediate grounds for complete ostracism (and running danger of being similarly destroyed) and, if it can be arranged, the removal of all Thread in the Threadwielder's possession.
They're not very prone to helping each other (they're more a live-and-let-live people), except to defend from other Threadwielders. The notion that other things might be able to do them harm is difficult to swallow and might take a few millennia to properly sink in; only to be so alien a concept that it registers as much more threatening than Threadwielder warfare, even though it's not, and does not invite intervention, either, just avoidance.
Their culture has an age-based hierarchy; the older you are, the more respected you are and the more influence you have, unless you've done something to earn contempt or derision.
Failing to correctly assess the consequences of one's Thread-based tampering is practically considered a heinous crime, since anyone who dares use Thread (= a lot of Threadwielders, but not most of them) ought to bloody well know what's going to happen for the next few millions of years at least.
Generally, despite perceiving time no different than a human being might, Threadwielders ignore short-term changes, where 'short-term' is anything under one millennium. If a problem persists for longer than that time, it's acknowledged as an actual problem. Before then, it's a nuisance at best - unless, of course, it affects them personally, in which case it's dealt with. If it's happening to other people, though, it can wait.