This thesis investigates quantum phenomena in superconductor-semiconductor junctions fabricated in a new material platform of in-situgrown parallel nanowires motivated by theoretical proposals describ-ing quantum states such as coupled hybrid states and topological effectsin such devices. Even though these two phenomena were not observedin these 1st generation devices, a systematic study of novel double-nanowire platforms was performed in various geometries. Initially, su-percurrent was studied through a parallel double quantum dot systemwhich was formed in a double nanowire Josephson junction. Minimalinter-dot coupling was found. Driven by the flux-induced studies infull shell nanowires, a first study of Little-Parks oscillations in doublenanowires was performed, showing that an ellipsoid cross section, suchone of double nanowires, can be fitted with good agreement using asimple model. The final study of double nanowires shown in this thesisinvolves multi-probe measurements of superconducting islands. Tem-perature analysis of the island resonances is well understood using athermodynamic model, and the behavior of the resonances points to-wards a common sub-gap state extending across the device. Finally,insight on the physics of a superconducting island in close proximityto a tunable quantum dot is investigated in a single nanowire, whereCoulomb-aided Yu-Shiba-Rusinov states are studied in various regimes.