I'm not a fan of the 66 hand. First, I would 3bet smaller. Villain opened to 4x, and was called and you made it 18xbb.. In this spot I would go a bit smaller to like 15-16bb, so like $0.75-$0.80ish.

However, I wouldn't 3bet 66 here. First, 66 is going to flop a strong hand very rarely. You aren't going to want to get 66 all in preflop, as that would be spew. You also indicate that both villains are lagtarded, so there is a good chance you will be getting called fairly often preflop. Which added to the low chance of you seeing a good board for 66, makes this a pretty trivial call and setmine spot for me.

I mean if you 3bet preflop and large cards come off, sure you can cbet, but if these villains have a piece they likely aren't folding. So when called you have very little equity, and not much fold equity either. Which makes for a pretty terrible bluff.