PdMX (M = Cr, Fe and X = Si, Ge) half-Heusler alloys, have been investigated in cubic C1(b) crystal structure which conforms to F (4) over bar 3m space group by using local spin density approximation (LSDA) within the density functional theory (DFT). Firstly, for all materials, the most stable structural phase, which is type-II phase, has been determined. Then, all materials have been considered in ferromagnetic (FM), paramagnetic (PM) and antiferromagnetic (AFM) orders in the most stable type-II structure. The estimated Curie temperatures by using energy differences between FM and PM phases in mean field approximation have been found to be noticeably higher than the room temperature. After the determination of the most stable magnetic phase, their full structural, mechanical, electronic, and lattice dynamical properties have been studied in the most stable magnetic and structural phase. The calculated electronic band structure and total electronic density of states (DOS) have showed that there is no band gap revealing metallic behavior. The estimated elastic constants and calculated phonon dispersion curves have confirmed the stability of FM phase, both mechanically and dynamically.