I have a decent image at a fairly soft table which has around 6 fairly weak players.

Hero LJ (decent reg) £400
CO (loose fish) £300ish
Button (loose reg) £200

Folds around to me in the Lowjack and I have Q J and I open to £6. CO and Button both flat.

Flop - 4 A 7 - Pot £21

Sick flop giving me second nuts. I am cbetting a ton of hands here so I lead £14 and both players flat. Obviously wary of plenty of Ks-x combos that either could definitely have.

Turn - 10 - Pot £73

Not the best card even though it gives me a royal draw. I check and HJ and Button both check. This is where I feel I made a mistake. Looking back I felt I should always lead here. I still have second nuts and a small bet of £45ish would let me see where I am.

River - 4 - Pot £73

River pairs the board and now I think I have to check given that all sets (however unlikely given the flop action) and 2 pair hands fill up. HJ bets for £60 and Button flats. I think for a moment since I am getting 3-1 but I don't think I am ever good here and then I fold.

Am I right that my turn check is terrible? And should I ever be calling river? I was thinking about calling the HJ bet but once button flats can I ever call profitably here?

I don't think the turn check is terrible. What spade are they calling with? Let them take a stab at it. I highly doubt they have two pair (esp with a 4 -- maybe A4) or a set, but it's possible.

I call river, but I don't mind the fold. Not sure how you can beat both of them.

I'd bet the turn - think worse hands are calling
and fold the river when a bet and a call have happened

If you bet the turn, is it a bet/fold? Do you give up on river? Give up to one of them or only if it's both of them?

Checking turn really makes me want to call river vs. weak players, but I need more specific reads to make sure.

If the other guy folded you should probably call but calling against 2 players is a bit optimistic.

I would recommend a blocker bet in spots like this. A FH is rather unlikely, higher flushes aren't too uncommon, but you have good equity and still want to see a showdown. Fire 1/3 pot and safely fold if raised. You'll also get looked up by worse

yeah if i bet the turn it's a bet fold
on the river i'd probably check call vs 1 player as the board pairs and happy to fold if there is still action from both of them

yeah i'd want to call river and would vs one person but with the 2 of them not sure i can really see us being ahead

Betting turn is really bad. Do not do it. If you're going to bet Qs here, do it without the Js, that's the prime hand you get value from, that and maybe sets.

You generally only bet turn with hands that you plan on getting 3 streets from and you're not going to do this here.

Finally, what combos of lower flushes can he have? Most lower cards are 2 spade hands which is much less likely now. Most hands he has that are offsuit have high cards (KQ AQ AJ KJ etc), you block the J, so there just aren't many of them. There's just about nothing that will call you here, since they're unlikely to have Tx9s. Just check.

If we bet turn, we almost definitely have to fold. Our range is very Ks heavy, and it's 3 way, we're just about never getting bluffed in this spot, plus we still have all our Ks combos so we're protected.

This was my exact thought process when I played the hand. Especially when it came to the river action. The Button who flats river should have a flush almost all the time. And I didn't think he has many 9s combos. For what it's worth I had the best hand. The button had AKos with no spade and CO mucked.

Having the (likely) winning hand is not always a reason to bet.