It's been a long time but here comes the updated language diagram, now with BK3!
BK1 & BK2 both speak English by default, except when they talk about what they play, which they still do in Arabic. They also speak German and French when the situation is right. The mix a lot when they speak with us, and even when they don't, the grammar more often than not is English.
It is called "majority language" for a reason. *sigh*
BK3 obviously doesn't speak so far. The girls will address her in whatever language is appropriate. They will speak Arabic with her if she is with Babelmum and German if she is with me. If BK3 is alone they will use whatever language first crosses their minds, I think.
We need more holidays in Algeria and Germany, I guess. Or more visitors.