Well, I’d be more charitable to the OP if the questions hadn’t been based on a novel already written. That’s just… strange. Also having opposite-sex parents lead them down the aisle: muh? Why? Because a gay man’s Dad becomes a woman? That’s a new twist on the nature-nurture debate.
I’ll answer anyway, because I’m bored, and maybe the OP genuinely was just woefully uniformed.
I’m gay, not married, but have been to numerous gay weddings.
If they had young children or were planning to have children together, they often changed their names in some way - either a completely new name, or one spouse taking the other’s surname - not based on butch or femme or whatever, but based on family allegiances, kids already born, or how nice the name is - or they took on a completely new name.
If there were no kids involved, no name changes took place.
I don’t know for sure if anyone carried the other over the aisle, but I suspect that it would have just been in a jokey way, like it would be with straight marriages these days.
None of them were ‘given away’ by their family. However, the same goes for most straight weddings I’ve been to. Quite a few of my gay friends who’ve got married haven’t had any parents there at all because either they’re dead or they’re not comfortable with the marriage.
Clothing can be a little tricky. One woman wearing a dress and the other wearing a suit would look, I don’t know, like the one in the suit was actually ‘the man’ in that relationship; even though that’s just how they’re comfortable dressing and that’s how they’d dress on other occasions, for their own wedding it’d be a bit too much of a statement.
So, generally, both women have dressed up a lot for the occasion, either both in dresses, or both in really nice trouser suits, or one in a dress and one in a trouser suit but neither looking like a wedding dress and a wedding suit. The clothing fits the colour scheme for the wedding just like a straight bride’s bouquet usually matches her groom’s tie.
Men have it easier in this regard - two men in wedding suits or just suits or tuxes or whatever looks fine, and that’s how they’ve dressed.
The other traditions have been made up as they’ve gone along, depending on how much family was involved, how much money, how traditional the couple were generally, etc.
They have, all but one, been more low-key than the straight weddings I’ve been to for people of the same age and income. This is partly because they have to be in a registry office rather than a church or some glamourous location. Some registry offices are pretty, but some really aren’t, and you have to be in and out of there pretty quickly.
I’ve only seen one lesbian wedding where one woman was in a wedding dress, the other in a morning suit and the whole traditional shebang was gone for. Funnily enough, that was also the only wedding where the family were with it completely from the get-go.