But isn´t the peasantry still the largest and the majority of the population? I don´t think it´s a 19th century thing at all, in this period mass literacy was becoming more present and public schools, a factor that in a sense could make speaking more languages possible as well.Mostly because you're thinking along XIXth lines, inspired by nationalism and exclusivism, IMO.
Long story short : countryside tends to be more unified linguistically, but is still pretty a patchwork especially in these regions with two communities possibly using different languages.
Making countryside only a matter of "peasant" compared to cities is also a non-sense : not dwelling too much on how rural elites can easily differ culturally from most of the population (even when using a speech close to the mass of rural population), and it's perfectly possible to see a Romance speaking elite ruling over an hellenophone community, you have as well to take in account the urban influence over its direct periphery (La Guardia), or the reverse (Ragusa).
And, of course, in a same village, you could see people coming from a neighbouring community not sharng the same linguistical or cultural features, altough we're less talking of a mutual influence there.
Without understanding this, it's hard to explain how SIicily was re-romancized, or the changes in the "border" between Romance and Germanic speeches in Northern France.
I don´t see how a large mass of people without any education and not working in cities, trade or being part of a elite can effectively speak more than one language(outside the exception I list in the other post).