Paquin confirmed that she was pregnant in April, but she and Moyer have so far said nothing publicly about the possibility of having twins.
Trammell, who is a father of twin sons himself, seemed to let slip that Paquin and Moyer will be having twins while speaking to Us Weekly.
"I'm so excited for them. We sent them a special gift. It's so interesting that True Blood has become, like, the 'twins' show," Trammell is quoted as saying.
He also spoke of his advice to the couple: "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!"
Paquin and Moyer's spokesperson has not yet commented on the matter.
Moyer is a father to two children from a previous relationship.
The True Blood couple married in Malibu, CA in 2010 after dating for two years.