The sensors on the I2C buss has an address. As long as there is no address conflict on the buss you can add multiple sensors. You need to check what address your sensors are using and/or the possibility to change the address of your sensor if you find that there might be a conflict.

@BartE, @martinhjelmare - this is sometime we should work with in the standard sketch. I have one relay on the edge and sometimes its having really hard to get that ack back from the controller and it never changes. It would be good if the relay made the switch, send the on/off to controller and waited for the ack. If you dont recieve it you send again and tries for some times.