Just an FYI, if your dogs have not used "doggie doors" before, your friends may need to be prepared to physically let your dogs out for potty time. Sometimes just getting dogs to eat or go potty when they are in a strange location (& especially without mommy!) can be difficult, much less expecting them to figure out how to navigate a trap door.
If they've visited before & are comfortable with the doors, or you have the doors yourself, then disregard.
Regarding your question, I've never had to treat my dogs for flea/tick before (knock on wood) but considering the health risks that can be posed from the flea/tick treatments to begin with, I would recommend staying with your regular protocol. Check with your vet about whether or not you should do something proactive or retroactive regarding ticks, if your normal treatment does not cover that. Have a good vacation! T. =-)