Thanks for sharing this hand. There is quite a bit to talk about, so let us take it street for street
Preflop
As others have already suggested, this hand should just be folded. Playing bad offsuit broadways to much is a pretty big leak in a lot of peoples games. If it folds around to you in late position, sure try to steal the blinds. If you face a steal from late position and get a good price, sure defend. But an UTG open range is simply to strong to get involved with KTo.
The issue is domination. Flop comes KXX, he has AA, AK, KQ or KJ, but he never has K9, K8 or K7. Flop comes TXX, he has AA, KK, QQ, JJ, AT, but he never has QT or JT. The fact, that SB called, makes it even worse, unless SB is a fish. Preflop is very important, because while preflop mistakes are in themselfes small, they tend to create a snowball effect. It begin as a small innocent snowball at the top of the hill, but at the bottom of the hill (the river), it has become a huge ugly pile of snow. This is basically the story of this hand.
Flop
You flopped a gutshot on a paired board, so kind of a bad draw. The first thing to notice here is, that your hand is not good enough to check-call, so if you are going to continue, it has to be with aggression, which can either mean leading (donk betting) or check-raising. Leading is unconventional, and a lot of people have knee-jerk reactions against it, but I actually dont think, it was a terrible choise here.
You are probably slightly more likely to have a J than the other two guys, and leading puts UTG in a difficult spot, because he has SB to act after him. So its quite possible, you can get UTG off a hand like AK or AQ, which would be a great result. Checking on the ofter hand keep more options open including to simply check-fold, if to heavy action develop behind you. So I dont mind either option here.
Turn
When you pick up
equity, you should usually continue to barrel on the turn, and in this case you picked up a flush draw. It can also be said, that Ac was a good scare card to continue
bluffing. However its not great, that they both called you on the flop, and its also not unlikely, that one of them actually connected with that card. If they have a flush now, you could be drawing dead, and even if they hit top pair, they are probably not going to fold it for one bet.
So I think, its probably pretty close between betting and checking again. However if you are going to bet, you need to use a size, which tell them, that you mean business. Something like 50-70% pot. They are not folding anything, when you give them 20:1, so this betsize is really something, you need to rethink. Its literally does nothing other than to dump 25c into the pot in a situation, where you are almost certainly behind to at least one of them if not both of them.
River
Now you made a flush, and you are likely to have the best hand, but I actually dont think, there is a lot of value to be had here. This is the point in the hand, where you really need to consider, what they have, and what you are trying to get called by. Or if it might even be better to check to induce bluffs. Ideally you would want them to have a worse flush or maybe a straight, but unfortunately that is very unlikely.
If they are good players, they are not playing KT, just as you should not have played it either. And they also dont play hands like A8 or 98 offsuit, which could have made an 8 high flush. They probably dont have trips either, because then you would have heard about it on the flop or turn. So if you lead out, you are trying to get called mostly by AX, which mean, you need to make it cheap. Instead you potted it, and that is almost turning your hand into a value
bluff. Your hand will often be best, but when you make such a large bet, you will only get action, when you are beat.