[NiHaoMike]

If the second TXV sources from the first TXV, there would be less flow to operate the ejector. And thus a lower efficiency. I can assure you the ejector works since the second evaporator gets colder than the first.

The "aspect ratio" of the phase separator is much taller than what the drawing indicates. The bulb for the third TXV is located pretty low so there's plenty of room for the liquid and vapor to separate. Also, the flow rate through that TXV is relatively low due to the low pressure drop across it. The first TXV is 1/2 ton as the design calls for, but the second and third TXVs are 5 ton as the larger bore is needed to get enough flow at the low pressure drop.

It does in fact draw from the cold and push into the hot. The dsPIC controls the water pump speed based on hot water temperature. It uses the local reading to run the PID loop, then uses the remote reading to make small corrections to the local setpoint. If the remote reading is unavailable or out of range, it simply reverts to only using the local reading.