@Tes yeux noirs,
There certainly is something strange.
You do not just get a visa for immigration to USA if you do not speak English - in this case the parents.
What does the OP mean by sterotypical education in Finnland? You learn first English and later French.
Yes Finns do speak with a heavy accent as they have difficulties in pronouncing certain sounds - not just in English.
The OP should only speak English with these two teenagers. Refuse to answer when spoken to in French or whatever language.