I don't speak Spanish fluently but when I was in school, they started our weekly Spanish lessons in kindergarden, it made high school spanish easy and better foundation for the ability to learn Spanish fluently. So teaching another langauge at a young age is important, I wish my school had been better about the Spanish thing, if they had I could probably speak it fluently instead of having to learn how to do that in college.

I would say as the others to talk in both, I don't think it will confuse them, I have friends who are bilingual and their parents spoke English and the other language around them since birth, never confused them they realized that one language was for home and the other for school.
Starting the learning of a launguage should start young, the older the twins get the harder it will be for them to learn it.

Good luck and best wishes
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