In this paper, we discuss the effects of metal dilution on the spin-crossover behavior of iron(II) solid solutions [FexNi1−x(bpp)2](NCSe)2 (bpp = 2,6-bis(pyrazol-3-yl)pyridine), including chemical synthesis, physical properties and light induced bistability aspects. For all the materials investigated, the thermal spin-crossover properties, T1/2, were measured and the stability of the photoinduced high-spin states was probed through determination of the T(LIESST) values associated with the light-induced excited spin-state trapping (LIESST) effect. It was found that T1/2 decreases with the metal dilution while T(LIESST) remains globally unchanged. These results were discussed and compared with previous results obtained in the same series with Zn(II) and Mn(II) used to substitute Fe(II). This comparison gives insights on the effect of the diluting ion size on the [T(LIESST), T1/2] temperatures.