What do I say?

My boyfriend just lost his godfather very suddenly. He really was like another parent instead of a godfather. He was there for every event, lived a couple of blocks away, and came around for dinner all the time. I know how to support my boyfriend through this.

However, his godfather was his parents’ very best friend for a million years, and I don’t know what to say to them. Do I get a card? I see them very frequently - do I just wait and say something when I see them next? What do I even say? On a scale of closeness, I’d put me and his parents at a 6-7. I don’t want to overstep but I do want to offer my condolences.