Got into a weird spot four-handed in a live $240 MTT

Blinds 6000-12000 2k ante Hero second in chips with 800k effective

Villian (btn)- limps
SB- completes
Hero (BB)- checks option with K7dd

Flop 325ddd (42,000)
SB: Leads for pot
Hero: calls
BTN: Calls

Turn: Qd (168k)
SB: Checks
Hero: bets 85k
BNT: Calls
SB: Folds

River: As (338k)
Hero: Checks
BNT: Shoves for 400k
Hero:?

Okay so i think pre flop is a fairly standard check behind BNT is almost never limp folding and is sticky in position SB is chip leader and a well below average player so I want to keep him in the pot especially with position. On the flop the SB never has a flush his range is almost exclusively straights and pair plus draw hands given how often we play together and reads i have on opponent. I think calling in the best play keeps all his dominated hands in and allows the BNT to call with similarly dominated hands behind me. When the SB checks on the turn i assume he's check folding all his straights and check deciding with hands that turned a flush. I think half pot is fine (maybe smaller is better?) The button tank calls and SB folds. The button typically acts quickly so i'm a little suspicious at this point but i assume 88d or 66d thinks a little before calling. I think my river play is terrible, although I'm suspicious that i don't have the best hand he has so many small to medium flushes that will check behind but would call a moderate bet size and if i bet something like 145-190k on the river i can pretty comfortably fold to his shove. I'll wait for some discussion to reveal results and appreciate as much feedback as possible.