Well, marriage (in some form or other) is a near constant in human cultures as I recall. At least historically, up to this point. Now, it isn't always between one man and one woman. Historically, one man and multiple women is a common model, but that is historically (more on that in a minute).
In Eve, I'm sure one man/one woman is still common. I suspect that other models are also fairly common, perhaps depending on where you look. I don't just mean which empire, but down at a more local level, particularly with empires that are less homogenous culturally (Gallente, Minmatar, most of the 'minor' factions, perhaps some places in the Empire.)
In the State, there is evidence of some cultural taboos, the one we know about for sure being homosexuality. On the other hand, there is heavy use of growing children in tubes. That means that in terms of reproductive strategy, women don't have to go through an entire pregnancy. I would be interested in finding out about the State's (or perhaps it would be by corporation?) position on abortion. If the attitude about homosexuality is population-driven, it suggests potentially a corresponding anti-abortion stance (particularly when they can grow the kid in a tube instead).
OFC given the ability to grow population on demand via tube child programs, a taboo on homosexuality seems maladaptive. Cultures do change only so fast, though. It may be rooted in the pre-diaspora (pre-tube-child) culture too, Caldari Prime not being the nicest place to live.
Anyway it seems to me that the tube child program essentially removes practical, reproductive issues for nearly any family arrangement. That doesn't mean the culture is in a place where people could actually take advantage of that (particularly in more conservative parts of the State). There might be more liberal corporations (not in the political sense, since Hyasyoda, for example, is liberal politically, but being one of the oldest corporations and run by the same family might have a more conservative culture internally, whereas NOH is 'practical' but strikes me as having a liberal internal culture) that are open to non-traditional models (whatever the traditional models are, for the Caldari).
There is also the issue of entirely new family models arising solely from tube child programs. One of my characters was raised in a crèche, and 'family' to her is siblings (some closer than others, not necessarily blood-related). In her crèche, there wasn't a strong parental bond with supervisors etc, so the extent of her 'family' is the other kids from the crèche. This gives rise to an idea of non-blood relations being 'family' in (to her) a very real sense.
This also means that her domestic arrangements growing up were not unlike being in barracks, with everyone living largely in common areas.
Outside the State, particularly in the Federation, I imagine that they have the tech for tube child programs, but not the Caldari cultural baggage. So, assuming someone can afford tube-growing, it opens up a great many possibilities.
I also suspect that whatever 'traditional' is for the Caldari, you see a lot of 'non-traditional' among the Guristas. Kinda the point, after all.
I suspect that in the State, setting aside the tube-kid part, there might be a lot of extended family living together. Probably also common in the Empire. I do wonder how things like inheritance are worked out in the Empire, since by all evidence there is essentially gender equality. Oldest child? What if there is a child from before a given marriage, and one from the marriage? Who inherits what? Seems like it has potential.
Others have a better grip on the Republic than I do, and I think the stuff that has been written about it is fascinating. I have thought a lot about Thukkers, and imagine it might be 'it takes a ship to raise a child' in many cases.
I wonder about people who travel far, often, but unlike the Thukkers not with their family. If you fly for the Cartel, say, and you only go 'home' once in a great while. Do those poor men and women in frigates in .5 Republic space have families waiting for them back in Curse? Husbands, wives, or some other arrangement (as doesn't seem unlikely with the Cartel) waiting, worried, for word from them?
I've a character (Hilion Narath) who is an ex-Cartel pilot. He never settled (and his family background was growing up with a large extended family of well-to-do commoners in the Kingdom) but surely there are pilots in that situation who do try to start a family, of whatever stripe. Maybe there are certain arrangements that would work particularly well, for that? Larger family groups for example, to provide support.