These dates are taken from a genealogy of the House of Bëor reproduced in volume XI of The History of Middle-earth (The War of the Jewels), and are not therefore strictly canonical, but they do fit the dates of other events described in The Silmarillion.
2
The published Silmarillion only shows the sons and grandsons of Boromir, but according to the extended genealogy in volume XI of The History of Middle-earth, he also had two daughters and three granddaughters. Of these, two were important in their own right, though they don't appear in any definitely canonical sources. Andreth played a role in the philosphical dialogue known as Athrabeth Finrod ah Andreth, while Bregil was the grandmother of the hapless Brandir of Brethil.