Villain is 50/12.5/00 (infinity) over 8 hands (virtually no history).

Full Tilt Poker $0.10/$0.25 No Limit Hold'em - 9 players
The Official 2+2 Hand Converter Powered By DeucesCracked.com

CO: $32.32
BTN: $5.00
SB: $5.00
BB: $33.82
UTG: $17.05
UTG+1: $5.00
UTG+2: $47.39
Hero (MP1): $25.00
MP2: $16.16

Pre Flop: ($0.35) Hero is MP1 with K K
1 fold, UTG+1 raises to $0.85, UTG+2 calls $0.85, Hero raises to $4, 1 fold, CO calls $4, 3 folds, UTG+1 raises to $5 all in, 1 fold, Hero calls $1, CO calls $1

Flop: ($16.20) 9 A Q (3 players - 1 is all in)
Hero checks, CO checks

Turn: ($16.20) 8 (3 players - 1 is all in)
Hero checks, CO bets $4.50, Hero ?

I think this board is too dangerous to check an ace or AQ two pair. I also discount AQo and lesser aces, which are often mucked utg and probably aren't coming along after your 3bet. I don't think AA is in their range b/c of no 4 bet preflop. The villain may like to 4 bet QQ preflop as well. I don't know if 99 or 88 is in their range. If they are a bad player, they might call your 3bet preflop with 88 or 99, but if they are bad enough to call your 3b with 88 or 99, I don't think they are good enough to open 88 or 99, and are more likely to limp this hand.

If they flopped a monster, they might check the flop, but put in a bigger bet on the turn to make it easier to play for stacks on the river.

I think they have a hand like 1010 or JJ and are making a semi-bluff stab at the pot. I am calling this bet and allowing them to make a dark tunnel bluff on the river that I will call as well.

What I hate about this hand that makes it complicated is that one person is already all-in, so even if you bet to try to shake me from the pot there's still one player all-in. You're not winning any more money unless I put more money in. I just don't understand this hand. Even if this person has TT or JJ, there's no benefit to betting

They are betting 6 outs if they have jj or 1010, although their set outs might be dirty. If they are a reg, they know not to bluff at this pot when the last preflop action was calling a scumbag short stacker's raise. But if they know that we are regs too, they know that they can bet into this pot, and we we will know they aren't bluffing, so they can use the added fold equity to get the pot heads up. Or they could be a donk who doesn't know this spot from any other, and has most likely already forgotten about the AI scumbag SSer, and is just betting b/c he thinks your flop check means you don't want the pot and can win the pot outright.

Either way. I think call/call>folding>raising

Why didn't you push over that 5$ shove? Calling with another person left to act creates situations like this.

Will it let you? If someone shoves with less than a minraise, are you allowed to raise on top of that?

You're right, its not possible to shove when someone shoves with less than a minraise over you.