PS
*-šVmV/-šVnV - their; them (genitive and accusative pronominal suffix, 3 pl.)
(Kogan 2009:70)
The shift *š- > h is distributed between languages the same way as in the realm of independent pronouns of the 3rd person.
The plural of the pronominal suffix of the 3rd person is based on the element š- with the extension -m- or -n- combined with more or less expressed vocalic oppositions (Kogan 2009:69). The character of consonantal and vocalic oppositions in individual languages generally corresponds to the nominative forms.