they aren't married yet, it was an engagement ceremony, a fancy way of making their relationship official and get both families to know each other a bit more before the actual wedding, kinda like a wedding before the wedding, their engagement can still be undone
>surprised that other love interests were introduced
you see them in a spread in chapter 1, don't overreact over it, but yeah, it was a bit rushed
and there better be a good reason as to why they like him, he might as well be a bread loaf so far