Preflop
I could see 65s being an open, but you really need enough fold equity to justify it. That could be preflop fold equity (limp-folding), postflop, or more likely a mix. I have a hard time believing you'd have enough at 1/2. Especially multiway. People tend to call too often and the generic formula for beating 1/2 is to just value bet a ton and only bluff very selectively.
Flop
I think that the cbetting is questionable. If Villains are limp-calling with about 20% of hands and continuing with all pairs, you only have about
30% fold equity. If you were semibluffing with some sort of draw, maybe you could justify it, but you don't really have any equity. In general, I think that in bluffing multiway at loose games, conditions need to be pretty pristine.
Turn/river
I could see a float being good here. One thing I've learned from Ed Miller is to pay attention to bet sizing tells. Such a small turn bet seems pretty weak and like a solid opportunity to float. And I like the float instead of the raise because you are last to act and you can use his river action to gain more info. Since he checked the river, yeah, I could see the bluff! It's a tough spot to tell because it's sort of a non-standard situation where you don't have a great history.