Hey guys. Some questions to this hand.

UTG: 18/14 reg. As far as I can tell he is straightforward, fastplays strong hands and rather nitty in general.
MP: 78/9 - obv not a strong player. What's relevant here: He just x/called twice 100bb deep OOP vs my cbets in a 3bet pot with 5JJK on 558r6ss, which makes me believe that he likely just flats strong hands on this flop.
BB: 60/30 over 10 hands. No reads at all.

Pre: With the fish in the hand I'm always calling. Would you call this if the fish folded? I'm not sure if such broadway hands are still playable if the suit is far from nutty.

Flop:
Even tho I'm never bluffing in this spot I feel like I pretty much have to raise here, although I am kind of concered about UTG cbetting here. Since I have the read that he is very nitty, I think he has a K here almost always (99 he play passivly). I don't see him cbetting QJT or AA here hardly ever.
MP will call here with K***, QJT, 99, and maybe even as weak as (QQ,JJ,TT)+gutter.
With those assumptions I want to raise b/c I'm hardy ever behind and there is lots of value against the K*** that either UTG or MP likely has. I'm worried about UTG tho since the K's that he raises UTG almost always have either an A or (/and) a 9 in it due to connectedness. 
Once I face the 3bet I know that UTG has mainly K9 here. Prolly some AK, KQJT, 99 as well. The fact that MP flats as well is reallly confusing. What are your assumptions here and how do we proceed?