This is what I heard (someone can clarify if I got something wrong, or can explain better) that for almost the whole time you're with your party. Then at the end, you're given a card, one for being in the seat, one for the bike, then the line is split into two at the very end briefly. You're standing right next to each other in the line. That is what has been described / what I've read.
For how it actual works, this is my theory. Think of it as FJ, how there is a regular queue line then SR line towards the end. Instead of you being all in one line and the singles being in one line. Think of it as, for example, if you're a couple, you'd be in the regular queue and your partner being in the SR line and each of you go one by one.
As for odd numbers (one again my theory how it'll work), for example, if there was three people, I would imagine the third would either sit in the bike, or car seat depending on what they'd want and sit behind who they're with and have a single next to that person, or they'd pair another odd pairing with one person sitting next to the other odd person and the pair behind. However, more than likely, it will be just easier to match singles with odd number groups, especially since it'd move the SR line faster.