- Host family of everyone's
- Host family of your's (I got this from Google Translator)
This is from Mirai Book 5.
Minasan (皆【みな】さん） means everyone, and it's mainly used as a vocative, just like you say in English, "Hello, everyone!" to people in front of you.
Hosutofamiri- no （ホストファミリーの） modifies Minasan. And in this case, the particle no （の） indicates the host family is in apposition to Minasan. (Ex. Rudolph, the reindeer = トナカイのルドルフ; My friend Kevin = 友達のケビン)
So ホストファミリーの皆さん refers to everyone in front of the speaker, who are host families of someone. It can be my host family, or yours, or theirs, depending on the context. The literal translation would be "everyone in (somobody's) host family".