The crystal structure, magnetic and magnetocaloric properties of (Mn,Fe,T)1.95P0.50Si0.50 (T = Co, Ni and Cu) compounds have been investigated. All the compounds crystallize in the Fe2P-type hexagonal structure. All these transition metal substitutions for either Mn(3g) or Fe(3f) weaken the ferromagnetic ordering, while showing complex effects on the energy barrier for nucleation in the first-order magnetic phase transition and result in complex behaviors in thermal/magnetic hysteresis. A first-principles density functional theory calculations show that Co, Ni and Cu atoms occupy 3f, 3f and 3g sites, respectively.