Very early in single table sit-n-go. Everyone has roughly the same chip count which is around 2000. Blinds 15/30

PF: UTG + 1: raises to 100
Hero raises to 300 from MP with J-J
Button calls 300
UTG + 1: calls 300.

Flop: Kd-Kc-3d
UTG goes all in (he barely covers both of us)

I have no information on the level of aggression of this player yet, nor the one behind me. I'm caught in the sandwich and eventually lay it down. Perhaps this is an easy laydown (especially with someone to act after me), but if villain had a king, does he really go all-in (not too uncommon to overbet a big hand)? if he smooth called preflop with QQ or AA, is he really comfortable blindly going all in in first position with 2 kings out there? This seems more like an A-Q of diamonds or pp anywhere from 8's to 10's, no?

Regardless i'm interested in comments to the above situation and I ask if your advice would have changed significantly had the button not been involved behind me. Thanks for your time.