"my question is: if they will be unschooled, there will be a long period of time that they will not be fluent in english (until 8 or 9 y.o maybe). so then, for the natural learning (of everything else, not the language) to happen (in unschooled setting), don,t they need to be fluent in the community language?"
I think honestly, you are the person here with the most experience of this.
All I can say is, based on having kids who are nearly 8 and nearly 10 which is around the age you're looking at for English fluency, that in terms of navigating their community alone, that doesn't happen so much at this age. We are fairly active in our community but I'm always there with the kids. I'm pretty hands off, and they are good at persuading adults to show them things, but it coudl easily be that the adults your kids connect with are ones who share their languages anyway. My kids also do kid activities (scouts, band etc) - some not in English, by the way, which seems to work fine though they are pretty monolingual.
I think for a teenager navigating their community alone - which is what I'd expect my older kids to start doing- fluency in English would be helpful although at the same time, they'd learn it if they needed it IMO. For a preteen I'd say the absolute best strategy is to have an interesting life yourself with as many interesting people as possible and share that with your kids. From what you've written your life sounds extremely interesting and very rich, and you have access, because of the language and culture, to a lot of stuff that other unschoolers would love.
Classes wise, my kids do several classes and band where English tends not to be the primary language spoken and its fine. There is a difference because everyone speaks English so its possible to translate for my kids if need be, though at the same time its not generally rocket science to work out what they need to do!
So in a nutshell, bearing in mind that you know more about this than any of us, if you think your kids will be fluent by around age 10, I wouldn't worry at all and instead I'd get on with giving them interesting experiences within your communities.