Well it says " All team members must have passports valid up until at least July 5th 2014. Finalists will be required to travel to Helsinki, Finland for the onsite finals. Any finalist who is unable to obtain appropriate travel documents, such as a passport or visa, may be disqualified from the onsite finals and an alternative finalist may be selected." https://helloworldopen.com/rules
so I would suppose that if you get to the finals (meaning to be in the top two teams of your region), then yes you must all travel to Finland, but expenses paid.
However, the qualifying rounds are organised via Internet, so the vast majority of teams will not need to travel. Of course Helsinki in June is a really nice place to visit if you want to come on your own and check out the finals live ;)