Live Stud8 Game. Folds to me in last position with (A2) A and I complete. The bring-in (XX) 5 calls

The bring in player is older and on the passive side. Misses value in some key spots but otherwise plays good. Is a decent winner in this lineup.
I think he never 2-bets me here and his range is 3 low, wired pairs 8 and lower, he might possibly fold 99-JJ, might not but def playing QQ/KK. He has all split 5's with a low kicker and most likley with a high kicker as well, though there is a very small chance he folds some of those to the bring in. He also has all 3 flushes but I dont remember the suits on this hand except that the boards were mostly rainbow

4th Street:
(A2) AK Check : Call
(XX) 57 Bet

I will check/call with my range here.

5th Street:
(A2) AK9
(XX) 579
'
On this street Im not sure what to do. Its very unnatural to lead this card after check/calling fourth. Also because my opponent semi-bricked I dont expect him to nessecarily keep betting, although he might. I think he leans towards checking because of his passiveness.

This is the question I have of whether I check/call, check/raise, or lead here? I think if I check and he bets I will check raise but I dont know whether its better to just lead this 5th street even though its awkward. How bad is it if it goes check/check?

Follow up questions from my opponents perspective:
1) If he has 4 low here on 5th against my board and I check, should he bet?
2) If he has a split/wired pair and 3-low on 5th against my board and I check, should he bet?

Thank you!