So neither of them are telling the truth so maybe both of them are guarding their doors that lead to the same place.
Hmm, good point.
This is too much thinking for a thursday, someone else figure it out.
Almost got it...
The answer is:
You will ask "What will the other one say is the door to heaven"? They should answer the same and you will choose the opposite door they say (if you want to go to heaven).
youve gotter let us guess it first