I'd like to know other player's reasoning on situations that involve a "dubious" river Bet or a check behind to conclude the hand.

Today I had 3 hands that unfolded quite similarly. (Everyone 100bb deep / all hands)

Hand 1 - QhQd
Hero CO raises 2.5bb with QhQd.
2 folds, BB calls.

Flop comes 6c5s8s (pot 5.5bb)
- BB donks 4bb
- Hero calls / raise ?

Turn comes 3h (pot 13,5 bb)
- BB checks / Hero bets 8bb / BB calls

River comes 6s (pot 29,5bb)

Board now reads 6c5s8s3h6s - BB Checks - Hero should bet QQ ? (as well as 99-TT-JJ ???)
If you bet (how much) and would you fold to a raise? Is check behind a good option now that river completed the flush and paired the 6?

Hand 2 - JhJs
HJ opens 3bb
Hero CO 3bets to 9bb
others fold

Flop comes 6s9s4c (pot 19 bb)
CO checks, Hero bets 10bb, CO calls.

Turn comes Ts (pot 39 bb)
CO checks, Hero bets 20bb CO calls.

River comes 2s (4 cards of "S" giving us J high flush) - pot 79bb.
CO checks - Hero remaining stack = 60~65bb - Shove or check behind ?

Hand 3 - KsJs
CO limps 1bb
Hero BU ISO 4bb
others fold

Flop comes 5hJh8d (pot 9,5bb)
CO donks 7bb / Hero calls

Turn comes As (pot 23bb)
CO checks / Hero bets 12bb / CO calls

River comes any brick not completing flush / not pairing the board
Pot now has ~45bb - CO checks - Hero checks behind = Thoughts ?

Any advice is highly welcomed.