Dear Katie,
Here is a census listing that includes a number of Vieira family members. If this is a match for your family, you may be able to use the other family names from Portugal to narrow the area to search in that country.
"United States Census, 1900," database with images, FamilySearch(https://familysearch.org/ark:/61903/1:1:M9TQ-GP7 : accessed 22 April 2017), Frank Vieira in household of John Perry, Lowell city Ward 4, Middlesex, Massachusetts, United States; citing enumeration district (ED) 791, sheet 2A, family 24, NARA microfilm publication T623 (Washington, D.C.: National Archives and Records Administration, 1972.); FHL microfilm 1,240,660.
It is possible that this group of people came to the USA together. Finding an immigration record might be a good next step for you. Hope this helps! -NGP