Dear The Janos,
Children of Hungarian citizens could inherit their citizenship.
However, grandschildren cannot (unless your parent who is a son or
daughter of an hungarian citizen would apply for citizenship). If the
son or the daughter was born before 1957, it is possible to apply only
if their father was Hungarian.
Hungarian Consulate in New Zealand
Hungarian Citizenship and Passports
However, the fact that your grandfather was born in Hungary doesn't
mean that he is an Hungarian citizen himself:
"All applicants of Hungarian descent who do not have one of the three
documents that undeniably prove their Hungarian citizenship ? i.e. a
valid passport, or a valid Hungarian personal ID document, or a
current Citizenship Certificate (issued from Hungary within the last
12 months) ? or those who left Hungary prior to 1 January 1972 and are
not in possession of a Hungarian Passport issued thereafter have to
undergo a citizenship assessment by filling in and signing the
citizenship application form.
The documents that need to be attached to the form are:
birth certificate of the applicant (with typewritten certified
Hungarian translation if the original is not in Hungarian);
a document proving marital status (marriage certificate or divorce
papers or death certificate of former spouse);
applicant's Hungarian parent's birth certificate (and/or any valid or
expired Hungarian passport, personal ID document, military ID) and
parents' marriage certificate (with typewritten certified Hungarian
translation if the original is not in Hungarian).
Note: Only the full versions and originals of all certificates are
accepted. The Consulate?General or Consulate can prepare certified
true copies of the original documents, if you prefer your original
certificates to remain in New Zealand.
A Hungarian passport can be issued only to Hungarians whose births
(and marriages, etc where applicable) are registered in Hungary. A
prerequisite for registering the applicant's birth is the prior
registration in Hungary of the parents' marriage."
Hungarian Consulates in Canada
The fact that you'll become an Hungarian citizen does not mean that
you could automatically work in all of the EU. Some countries (e.g.,
the UK) allow Hungarians to work, while others require application for
a work permit. If you;d like a job permit anyway, it might be best to
just apply for a job permit at the relevant country's consulate.
I hope this answers your question. Please contact me if you need any
clarification on this answer before you rate it. I also recommend that
you'll search and read previous answers given here on EU citizenship:
EU + Citizenship + politicalguru (that's me)