Oh and for the logic:
D1 - Leading to Hell, Guarded by T1
D2 - Leading to Heaven, Guarded by T2
Lets say T1 is the liar and T2 is the truthful one.
T1, D1 - Yes
T1, D2 - No
T2, D1 - No
T2, D 2 - Yes
Doesn't get you anywhere, you could ask either one and wouldn't know for sure, however if you ask the twin what the other twin would say:
Asking T1 pointing to D1:
T2 would reply with No. T1 must lie and says Yes.
Asking T1 pointing to D2:
T2 would reply yes, T1 must lie and says No.
Asking T2 pointing to D1:
T1 would say Yes, T2 tells the truth and says Yes.
Asking T2 pointing to D2:
T1 would say No, T2 tells the truth and says No.