DemNotPP: Personal pronouns and demonstrative pronouns are separate classes, and they are not etymologically related.
In Hungarian, the third person singular personal pronoun (ő ‘he/she/it’) is derived from the PFU *sɜ ‘he/she/it’ word. The third person plural personal pronoun is an analytic form where the general plural marker -k is attached to the third person singular form of the personal pronoun. The demonstrative pronouns (ez ‘this’, az ‘that’) come from the *e and *o demonstrative stems (UEW I: 67‒68, 332‒333). There is no etymological relationship between the two pronominal categories.