Well perhaps a coffee or tea or some dinner? The point is get to know them well. This way you have some idea of who the kids are friends with and you can discus your concerns with their friends parents. On that note remember that values do vary. I think it is healthy to expose kids to a variety of people so while obviously I would not let a kid stay with anyone doing anything illegal or grossly immoral, a family that has adults enjoying a wine with dinner hardly encompasses this. But then I was raised by european Catholics so a few drinks are not seen as so bad.
On a sideline note when I was in my teens and early 20s some of the kids from homes where alcohol was strictly forbidden were pretty hardy drinkers. While I was not a saint, I did not do anything silly like get into the car with drink drivers because I knew my parents would not ground me for life because I had drunk 1 too many. This sort of thing sounds like it is a loong way off for you though
On a sideline note when I was in my teens and early 20s some of the kids from homes where alcohol was strictly forbidden were pretty hardy drinkers. While I was not a saint, I did not do anything silly like get into the car with drink drivers because I knew my parents would not ground me for life because I had drunk 1 too many. This sort of thing sounds like it is a loong way off for you though