Generally, the answer is yes if they will be paid for playing because it counts as employment. The best thing to do is check the state department website and look up the countries to which they will travel since visa requirements vary for each country and by country of origin.
More than likely, the answer is yes. Depending on the type of band, if they're students, they'll probably need student visas. If the band is getting paid for their performance, they'll need a work visa.
Generally, visas are required for bands to play concerts in another country. They need to apply for visas from their country or at the airport just like any other foreigner (though it is a lot easier for musicians to get visas for performances)
Yes, Visa's are required even if they are playing. The rules are the same for if someone were to go on vacation into another country for a long period of time.
