I can do it reliably in 6 Questions:
Ask the following question four times:
If I ask the next person if they are the Riddler, will they say 'Yes'?
If the Riddler answers the question and the next person is the Penquin, he will say 'Yes' otherwise he will 'Pass'.
If the Penquin answers the question and the next person is the Riddler, he will say 'No', otherwise he will 'Pass'
If TwoFace answers the question, he will 'Pass' if the next person is the Joker, otherwise he will answer 'Yes' or 'No'
If Joker answers the question, he will just answer 'Yes' or 'No'
This will tell us some thing about the order and might actually tell us what the order is:
If the Joker follows TwoFace, then we will have two Passes together, the first from either the Riddler or the Penguin, and the second from TwoFace.
The previous answer, before the first 'Pass' will tell us whether the Penguin is before or after the Riddler, e.g.
Yes,Pass,Pass,No - would be Riddler, Penguin, TwoFace, Joker
and ...
No,Pass,Pass,No - would be Penguin, Riddler, TwoFace, Joker
alternatively:
If TwoFace follows the Joker, then there will be only 1 'Pass' (the Penguin or the Riddler) which will identify the Joker, but TwoFace will be the next person, so:
Yes,Pass,No,Yes - would be Riddler, Penguin, Joker, TwoFace
Likewise,
No,Yes,Pass,No - would be TwoFace, Riddler, Penguin, Joker
So anything ordered similarly to the above will only need 4 questions.
Other orders are dealt with as below:
Otherwise, the Riddler and the Penguin will be alternating with TwoFace and Joker, and there will be two Passes, one from the Riddler, and one from the Penguin. So in this case it is simply a matter of telling the Joker from TwoFace, after the second 'Pass' answer is given - and then telling the Riddler from the Penguin
If you ask TwoFace/Joker, 'Will the Joker tell me the truth?', TwoFace must always 'Pass', the Joker must answer 'Yes' or 'No'
If you ask the Riddler/Penguin, 'Will the Penguin tell me the truth?', the Riddler will always answer 'No', the Penguin will always answer 'Yes'.
Bonus: No one will be asked the same question twice.
So, Batman can work the order out in a maximum of 6 questions.