Sky Sports revealed earlier this month that a host of Premier League clubs, including United, Manchester City, Liverpool and Chelsea were all chasing Filipe and Virginia.
Winger Filipe, who has been labelled the "the next Cristiano Ronaldo", and goalkeeper Virginia are regarded as two of the best young talents to emerge in Portugal in recent years.
Barcelona have already seen one offer rejected for Felipe with Benfica desperately trying to tie down the two teenagers to long-term deals to secure their futures.
However, United appear to have stolen a march on their rivals by coming to an agreement with Benfica to take Filipe and Virginia on trial so that they can cast an eye over the pair at close quarters.
If the duo impress during their stint at Carrington they could be offered deals to move to Old Trafford on a permanent basis.