Magnetic, electronic, and structural properties of MFe2O4 (M=Mg,Zn,Fe) ferric spinels have been studied by Fe57 Mössbauer spectroscopy, electrical conductivity, and powder and single-crystal x-ray diffraction (XRD) to a pressure of 120 GPa and in the 2.4-300 K temperature range. These studies reveal for all materials, at the pressure range 25-40 GPa, an irreversible first-order structural transition to the postspinel CaTi2O4- type structure (Bbmm) in which the HS Fe3+ occupies two different crystallographic sites characterized by six- and eightfold coordination polyhedra, respectively. Above 40 GPa, an onset of a sluggish second-order high-to-low spin (HS-LS) transition is observed on the octahedral Fe3+ sites while Fe3+ occupying bicapped trigonal prism sites remain in the HS state. Despite an appreciable resistance decrease, corroborating with the transition to the LS state, MgFe2O4 and ZnFe2O4 remain semiconductors at this pressure range. However, in the case of Fe3O4, the second-order HS-LS transition on the Fe3+ octahedral sites corroborates with a clear trend to a gap closure and formation of a semimetal state above 50 GPa. Above 65 GPa, another structural phase transition is observed in Fe3O4 to a new Pmma structure. This transition coincides with the onset of nonmagnetic Fe2+, signifying further propagation of the gradual collapse of magnetism corroborating with a sluggish metallization process. With this, half of Fe3+ sites remain in the HS state. Thus, this paper demonstrates that, in a material with a complex crystal structure containing transition metal cation(s) in different environments, a HS-LS transition and delocalization/metallization of the 3d electrons does not necessarily occur simultaneously and may propagate through different crystallographic sites at different degrees of compression.