Understanding the physical properties of a material is crucial to know its applicability for practical applications. In this study, we investigate the phase stability, elastic, electronic, thermal, and optical properties of the ternary alloying of the scandium and yttrium nitrides (Sc1-xYxN) for different compositions. To do so, we apply a "density functional theory (DFT)" based scheme of calculations named as "full potential (FP) linearized (L) augmented plane wave plus local orbitals (APW + lo) method" realized in the WIEN2k computational package. At first, the phase stability of the investigated compositions of the mentioned alloy is determined. The analysis of our calculations shows that Sc1-xYxN alloy is stable in rock salt crystal structure for all investigated compositions. Next to that, the elastic properties of the rock-salt phase of the studied ternary alloy Sc1-xYxN at all above said compositions were done at the level of "Wu-Cohen generalized gradient approximation (Wu-GGA)" within DFT. However, Trans-Blaha (TB) approximation of the "modified Becke-Johson (mBJ)" potential is also used in combination with Wu-GGA where the thermal properties are calculated at the level of the "quasi-harmonic Debye model." The obtained results for the absorption coefficients, and optical bandgap, represent that the title alloy may be a suitable candidate for the applications in optoelectronic devices.