BTN is on the LAG side but seems to have some idea about stacks/position/etc. SB is from Romania and seems kinda bad (3x opens, calling wide OOP, a little passive). I haven't been doing much, although the previous orbit I raise-called with J9s from CO vs. a 5 BB shove, so they might not give me credit for a narrow range here.

Both of them flatting the flop kind of freaked me out tbh. What do we do on the turn, and what's our plan vs. further action?

Poker Stars $100+$9 No Limit Hold'em Tournament - t150/t300 Blinds + t25 - 8 players

Hero (UTG): t11709 M = 18.01
UTG+1: t8500 M = 13.08
MP1: t9366 M = 14.41
MP2: t10200 M = 15.69
CO: t9380 M = 14.43
BTN: t16529 M = 25.43
SB: t13148 M = 20.23
BB: t6830 M = 10.51

Pre Flop: (t650) Hero is UTG with Q A
Hero raises to t675, 4 folds, BTN calls t675, SB calls t525, 1 fold

Flop: (t2525) 8 9 Q (3 players)
SB checks, Hero bets t1535, BTN calls t1535, SB calls t1535

Turn: (t7130) Q (3 players)
SB checks, Hero ?

i'm b/c'ing and not thinking much of it.

would expect btn to raise sets on this texture, he shouldn't really have 2 pair hands in his range, JT is a possibility but that's about the only hand you're behind that makes sense.
i'd also expect someone passive like SB to have a wide range pre, would expect them to raise sets/JT OTF so i'm least worried about them.

9.5k eff OTT i'd probably go 4600/c.

the first flat may be a problem but the 2nd flat never has you beat ever

i bet ~3.5k/call shoves

Yeah bet 3k-4k and call shoves imo.

You could take some different lines on the turn if you feel like you need to get creative, like betting really small, CR or sth, but it doesn't seem necessary.

Plus if you get a call you have a nice little shove the river and get paid off stack.

b/c, not particularly close