If Dracula stops in a location where Hunters are (regardless of the use of Double back), he has to fight them during the Action Phase, you're right.
If Dracula crosses a city where some Hunters are... I think the only way you are able to do this is by using the card that allows you to move twice in a round, and your first movement is via Double back (sorry, I don't have the game with me and I'm not able to check the name of the card). Anyway, the double movement is not a double turn. A turn consists of two different phases, Movement and Action. You place encounters / fight Hunters only during the Action Phase. If you move twice, you have two movement phases and one action phase after the second movement. So, let's say you are allowed to move twice in the same round. The first movement is a double back on Hunters city. You play your power cards, take the location card from the Trail / Catacombs (with all rules and restriction this implies) and that's it, even if there are Hunters in that city. Then you do the second movement, according to normal rules
Hope this helps!