Sub-Neptune exoplanets, with radii between roughly 1.5 and 4 Earth radii, offer tantalizing clues to the formation pathways of planetary systems. Two such pathways can be distinguished: twin and cousin planets. Twin planets are thought to form in a disk dominated by gas so that their solid-body cores grow slowly and the bulk composition is dominated by hydrogen and helium-rich envelopes formed by the accretion of gas with possibly a modest contribution of solids. In contrast, cousin planets, often referred to as super-Earths or mini-Neptunes, are thought to be formed in a dust- and ice- dominated environment with rocky cores that rapidly grow by the efficient accretion of solids before acquiring smaller hydrogen- and helium-rich atmospheres. However, the nature of sub-Neptune exoplanets is still poorly constrained from observations, mostly due to the degeneracy between bulk interior properties and atmospheric properties. Here, we present a tool based on the probabilistic occurrence of exoplanets in different planetary systems, which we apply to a subsample of the Kepler sample to statistically distinguish between the twin and cousin scenarios for the subset of sub-Neptune exoplanets observed by Kepler. We find that this can only be achieved by considering the population statistics, with the occurrence rate of twin planets showing much larger variation between systems than that of cousin planets.