Without knowing anything about the 5 seat, it is a judgement call on the 6th street fold, given that you must think he has a set of Qs or As (or unlikely, the other Ks). I would never check-raise 5th. I am uneasy with a big pair on 3rd street in a multiway pot, and I certainly am not going to give away the fact I have a little something by making the pot huge here.

I would have on 5th:
A) checked and called to see what developed, there are a lot of cards my opponents could hit here on 6th that I would have to fold to, and I'd like to see 6th as cheaply as possible (or check raised if 7 passed and I got a bet from one of the other two seats, preferably to get the hand heads up).
Or B) I would have led, and maybe the 7 seat would clear the field a bit.
Two bare kings with the 3 diamonds is not a hand I want to be hammering heavy in this spot.

Unless the 7 seat has a lot of notes from you involving the words 'idiot', 'donk' or 'retard', I think the fold is fine.