Three new nickel-based representatives of the so-called “layered hydroselenite” family have been characterized by single-crystal X-ray diffraction. In addition to the (enH2)[Ni(HSeO3)2Br2], the last missing member of the ethylenediammonium – transition metal hydroselenite-halide family, we were able to characterize the first members of a new family of compounds based on the N,N′-dimethylethylenediammonium cations, (dmedaH2)[Ni(HSeO3)2X2], X = Cl and Br. We compare the structural peculiarities of layered hydroselenites “stuffed” by the (enH2)2+ and (dmedaH2)2+ cations and predict existence of new series in this peculiar layered family.