The ability to establish coherent communication channels is key for scaling up quantum devices. Here, we engineer interactions between distant polaritons, hybrid spin-photon excitations formed at different lumped-element superconducting resonators within a chip. The chip consists of several resonator pairs, slightly detuned in frequency to make them addressable, capacitively coupled within each pair and inductively coupled to a common readout line. They interact locally with samples of PTMr and Tripak${}^{-}$ organic free radicals, deposited onto their inductors, which provide model $S=1/2$, $g\simeq 2$ spin ensembles. Frequency-dependent microwave transmission experiments, performed at very low temperatures, measure polariton frequencies as a function of magnetic field in different scenarios. When only one resonator within a pair hosts a molecular sample, the results evidence that spins couple remotely to the empty LER as well as to the local cavity mode. If both resonators interact with a spin ensemble, the magnetic field tunes the polariton frequencies relative to each other, on account of the different spin-photon interactions at each LER. When polaritons are brought into mutual resonance, the microwave transmission spectroscopically resolves an avoided level crossing that evidences a polariton-polariton interaction mediated by the circuit. Then, pump-probe experiments reveal that the excitation of a polariton within a connected pair is indeed felt, thus it can be read out, by the other one. Model calculations, compatible with the experimental parameters and results, suggest that the system excitation eigenstates show photon-photon and spin-spin correlations and entanglement near the polariton-polariton anticrossing.