The second is Ser Gerold Hightower, the actor who played him has confirmed this on Twitter.
@EddieEyre: 'Gerold Hightower' was on my contract if that helps :)
Ser Oswell Whent was apparently in Dorne and died there but it's unclear when or how this happened but it must have been around the time of the Tower of Joy too. In Season 4 Episode 1, "Two Swords", we see Joffrey leafing through the Book of Brothers. He stops on Ser Arthur Dayne's page but the page on the left looks to be that of Ser Gerold Hightower. It says the following:
Died in the Red Mountains of Dorne alongside his sworn brothers, Ser Arthur Dayne and Ser Oswell Whent.
After refusing to bend the knee to the new king Robert Baratheon, all three were defeated by a small force led by Lord Eddard Stark of Winterfell.