This isn't normal. It's weird and borderline creepy IMO.

You've known this couple for less than a week, if I'm understanding you correctly. You "hung out" for a few days last summer. You're travel acquaintances.

they are having a destination wedding, to which they invited us so of course we will go.

Why "of course"? I mean, sure, go if you want to, but there's no obligation here. You barely know these people. You make no mention of having any contact with them since last summer, now suddenly out of the blue they invite you to their wedding and then ask you to be their attendants--what, these people have no friends or family? People they've known for, you know, longer than a few days, to stand up for them?

we said yes, because how do you say no to someone who wants you to be a part of their wedding.

As Nancy Reagan put it, "Just say no".