By Humeyra Pamuk and David Brunnstrom WASHINGTON (Reuters) -U.S. Deputy Secretary of State Wendy Sherman and U.S. Ambassador to Australia Caroline Kennedy plan next month to visit the Solomon Islands, where their fathers fought in World War Two and the United States is in a modern-day battle for influence with strategic rival China. Sherman and her delegation will commemorate the 80th anniversary of the Battle of Guadalcanal during her Aug. 6-8 visit and meet with senior officials “to highlight the enduring relationship between the United States and Solomon Islands” and plans to open a U.S. em…