Uncertainty in annihilation?

Good evening /sci/, I'm currently still in school with the intention of studying Theoretical physics next year, hopefully at Imperial College London. In our physics class this morning, we were covering the creation and annihilation of particle-antiparticle pairs, and one of my peers raised an interesting question. Take for example the annihilation of an electron-positron pair. Upon annihilation two gamma photons are released.The question raised was that if the position of a photon is an event which will be determined probabilistically, how is it that we know that the outcome of this annihilation is indeed two gamma photons travelling opposite directions?

Conservation of momentum.
Nothing prevents the creation of 3 or more photons.
I don't know how the experimentalists would go about verifying this... bubble chambers?