My parents will be visiting the USA on a B2 visa. Before coming to the US, they will be staying at my sister's place in London for a month. My parents already hold a valid visa for both the UK and USA, applied and stamped in India.
Do my parents need to carry any other document for when they arrive at the port of entry at the Minneapolis airport from London?
Aside from the passport and visa, having a printed itinerary showing when they'll leave the country again, can often be a help (or even be a requirement) when at immigration in the states. Specially on a first visit.
There is no requirement to carry any other documents and anything extra is extremely unlikely to be required. However, if there is doubt about your motives for entry being what you claim them to be, evidence of a reservation for at least the first night of your stay may be helpful, along with a return ticket.
In the very unlikely event things really do hot up at interview, tickets for Walt Disney World or whatever may help to establish that you really are a visitor rather than a would-be illegal immigrant.
No, their passport and blue customs form they get on the plane is all they need. TIP: ideally place the form inside the passport at the page with the visa.
A return flight confirmation could come in handy as well, but I've never brought such a thing and never been asked for it.
