The two had earlier this week began a family trip with Billie's dad Bryan Lourd, who was married to her late mother Carrie Fisher for three years in the '90s, and his husband Bruce Bozzi, who posted a photo of the group and another man on a boat, wearing green face masks.
"The family that masks together lasts together!" he wrote.
Billie and Taylor, who play love interests on Scream Queens, first sparked real-love romance rumors in early December after co-star Keke Palmer posted a photo of the two making out on Snapchat. They have never commented on their relationship.
Taylor has been there for Billie as she deals with the deaths of her mother and grandmother, actress Debbie Reynolds. The two passed away within days of each other in December.
The two visited the Antelope Valley California Poppy Reserve together late last month. In February, they celebrated Taylor's 25th birthday, wearing matching onesies.