Can Dracula play "customs search" if a hunter is jumping from eastern to western europe using "sense of emergency"? What about jumping from a sea zone to eastern / western europe?
You can play Customs Search in response to a Sense of Emergency so long as the starting and ending locations are different areas of Europe and the ending location had no encounters.
You can't play it when a hunter is moving among sea zones as sea zones are not technically part of Western or Eastern Europe. You would have to wait until the hunter Disembarked somewhere and then play it.
Can hunters form a group and use "sense of emergency" together? If yes: who pays the cost
There is no official ruling on this as far as I know but based on the intent of Hunter groups (i.e. riding a train) I would say that yes this is legal. I'm less certain on the cost. I would lean towards every hunter paying the cost (after all they are all moving/warping) meaing they all also need to have enough health to do so. To me this seems to best keep the balance of the card.
I guess you could also argue that either the card's owning player only or the group's choice of hunter could pay the cost - but I personally like those rulings less. Really house rules at this point.
However if Dracula were to then play Customs search every Hunter in the group would lose their item cards.