As they explain it, you create 2 pairs of entangled photons. Grab one from the first pair and send it to Victor. Take the other one and send it to Alice.
Now grab one from the second pair and also send it to Victor. Grab the other one and send it to Bob.
It seems that depending upon how Victor measures his photons determines whether or not the ones that Bob and Alice get are entangled. Moreover, this is the case even if Bob and Alice conduct their measurements first.
The part that’s not clear is how does Victor do his measurements to create or not create an entangled state?