KJo is to weak to 3bet bluff against a strong UTG range. You had only 59 hands by him, it's just simple not enough to have decent reads. I would consider to 3bet with KJs, like KQs, QJs, J-10s.
We had a coldcall from the button, and UTG also called your 3bet. It was a 3way pot. Ok, the button player probably was a fishy, but his coldcalling range is close to the same as a regular's coldcalling range, some cards like AQ-AJs, maybe suited broadways, and pocket pairs. Against 2 opponents in a 3bet pot there are not enough FE on this flop, your flop cbet sizing was also too small to make them fold overcards. No cbet/f is the game, preflop I fold KJo too.
I think you narrow his range pre to hands that dominate you if you 3 bet. You can make an argument for calling and taking away on the flop or turn when you both miss, but you can make the same argument with 67s or A5.
You lose nothing if you fold pre, but stand to win a small pot on anything less then a KKJ or a QTA board. If it is pair vs pair, what do you think you are ahead of?