Two POE devices on One Ethernet Cable via a Y splitter
The POE specification does not allow for Y-splitters. Y-splitters do not follow the ethernet specifications either, and are a hack, it degrades your signal on the data lines. 

If you used a Y-spliiter the PSE can't determine what class of load it has, and you also run the risk of overloading the rated current in the cable with two devices.

Don't use Y-splitters.