There are many stories of a child speaking several languages when his parents speak different languages.
But languages can differ significantly, so I'm curious whether pairs of 'incompatible' languages exist.
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There is no limit on how similar or different two languages have to be for bilingualism. The historical experience suggests that this is not even a very good question to ask. There are millions of people bilingual in languages with completely different lexical bases, different syntax and morphology as well as phonetics.
Also keep in mind that: