Again, this is possible because what we (matter observers) picture as different spacetime processes spreading at the speed of light through the universe is an indivisible ensemble, an instant action/reaction event for the massless quanta involved.

No matter how far appart or for how long they've been "travelling out there", they describe light-like paths in spacetime, so their proper time is always zero, and they don't experience any distance or duration. So all the different emission-flight-detection processes that span from a common emission event at the speed of light from our perspective experience a single point/instant of existence from their own perspective.

Even if they end at different times and places for us, they all share the same instant blink of existence, somehow.

They appear to be part of a single particle at two different places at once because the correlations that we can observe in spacetime lets us glimpse their true instant nature. When we detect them, each one tells the story of the constraints and correlations that took place in our spacetime, how the locations and intervals we perceived are related to each other from the POV of their instantaneous entangled existence.