If the question is about your parents as individual people: Italians
If the question is about your parents nationality: Italian
~ It’s all about the context ~
22 กันยายน 2021
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Both are technically correct but 2 is more natural. It sounds more authentic and it´s what a native speaker would say.
23 กันยายน 2021
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Both! In 1 "Italians" is a noun. In 2 "Italian" is an adjective. This is not true with all nationalities, but it does work in this circumstance and several others.