  One goal in the quantum-walk research is the exploitation of the intrinsic
quantum nature of multiple walkers, in order to achieve the full computational
power of the model. Here we study the behaviour of two non-interacting
particles performing a quantum walk on the line when the possibility of lattice
imperfections, in the form of missing links, is considered. We investigate two
regimes, statical and dynamical percolation, that correspond to different time
scales for the imperfections evolution with respect to the quantum-walk one. By
studying the qualitative behaviour of three two-particle quantities for
different probabilities of having missing bonds, we argue that the chosen
symmetry under particle-exchange of the input state strongly affects the output
of the walk, even in noisy and highly non-ideal regimes. We provide evidence
against the possibility of gathering information about the walkers
indistinguishability from the observation of bunching phenomena in the output
distribution, in all those situations that require a comparison between
averaged quantities. Although the spread of the walk is not substantially
changed by the addition of a second particle, we show that the presence of
multiple walkers can be beneficial for a procedure to estimate the probability
of having a broken link.
