the reasons for ventilation in a house are to avoid condensation, and to provide nice air for humans to breathe
Since the house is unoccupied, having nice fresh air to breathe is not an issue
As regards condensation, there wont be any, as there will be no cooking, humans breathing, washing machines, dishwashers, clothes drying etc going on.
It doesnt make any difference whether you open the vents or not.....
In any case, since the house is old, there is probably a lot of ingress of air from the outside coming into the house, the house will probably be very well ventilated whether you open the window vents or not