I think it would be easiest if you could find a neighbor to come by & check on them at least once a day. While it may be possible to supply them with enough food/water for a week at a time, there's always Stuff that can happen and it would be best to have someone check on them daily. A neighbor who could just walk over could be easiest. Make their chicken chores as easy & simple as possible, allow them to take home all the eggs, and bring them a nice souvenir from your travels. Bon voyage!