WASHINGTON — Hunter Biden has joined meetings with President Joe Biden and his top aides since his father returned to the White House from Camp David, Maryland, on Monday evening, according to four people familiar with the matter. The president’s son has also been talking to senior White House staff members, these people said.While he is regularly at the White House residence and events, it is unusual for Hunter Biden to be in and around meetings his father is having with his team, these people said. They said the president’s aides were struck by his presence during their discussions.