A couple of suggested changes in your English original -

Question

Buenas tardes Shui e Inma ...It might be worth considering ... >> ?1. > "As many Irish people emigrated to the United States..." [because that corresponds better with the 'emigraron' in your Spanish translation].2. [Debatable !] > I first wondered whether "Halloween is really an ancient Irish holiday" might have been more helpful to us, rather than saying "... ancestral..."]... In Castillian, 'ancestral' is indeed sometimes used as a synonym for 'antiguo' - but perhaps there is a very slight difference in Englsh? Eventually, however, I could see that the use of the word 'ancestral' in that context was at least pointing us in the right direction.

Accepted Answer

Hola David and JohnWe are changing the verb to "emigrated" as you suggested. As per the adjective "ancestral" in English, we used the same word in both languages to put you in the right direction, as you said, and avoid other words that are synonyms. Using "antigua" would have of course been correct too. Gracias y saludos

Answer

I must agree, in the english, the words "many Irish people immigrated to" didn't work for me, and the spanish translation was most definitely emigrate.