"2 limpers to me in the bb, with the 4 straddle on.... We make it 20." 1/2/4 + 4 + 4 => 15 already in there...
I'd almost play Pot Limit on this preflop so agree with the making it ~24 pre (maybe a little higher IF we want to negate the psychological positioning of only having to put an even £20 / 4 red discs in). This is compounded especially if the straddlers playing ~100 and feels like getting it in, meaning he can only ever 3 bet shove to our raise.
As played i'd likely check back the flop too, a lot of people's ranges in this spot are suited (potentially Broadway) connectors so we're likely to be seeing two pairs / flush draws and straights looking to get it in. You say, "as am ahead of their pre flop peeling range alot.", but is this still correct for their 3 bet peeling ranges? Have they been frequently calling 3 bets? particularly a cold call from the straddle seems particularly more focused in the range of broadway / medium pair type hands? so i'd be more bothered about his holding in the hand.
If we check back the flop and the straddle bets we can evaluate our decision based on the "old ladies" decision...
We can profitably check call... but we can't profitably bet / fold...the only time we're ever profitably betting the flop is if we get both players to fold or we're betting for value and we're doing neither on this board texture.
As played we leave ourselves with an awkward turn decision where we could be getting trapped by either villain. The bet sizing of the straddler on the turn seems very valuey particularly if he's leaving 1/3 behind, this is so infrequently a bluff and may be leaned more to induce a call from both villains to gain additional value on close to nutted hands. If we call we're folding nearly every river.
While in game it sometimes seems counter productive to raise pre and check back these flops with a strong holding we can improve our pot control and not have to check fold our second street when we see cards like the

or paired boards; while we can also effectively balance our range if we similarly check back our nutted hands. This also gives us better contingency on the flop as we are never likely calling a raise on this board texture with our holding.