Paquin, 29, married her "True Blood" co-star Stephen Moyer, 42, nearly two years ago. They announced Paquin's pregnancy in April, but the news she is expecting twins wasn't public until now.
"I'm so excited for them," cast member Sam Trammell, who is father to 11-month-old twins Winston and Gus, told UsMagazine.com.
"We sent them a special gift. It's so interesting that 'True Blood' has become, like, the 'twins' show," Trammell said. "It's harder, having twins, but it's all we know. So we're trying to impart some decent wisdom. ... I told them to hold on tight!"