Dolphins centre Jack, who missed the start of the season with an ACL recovery, has won all of his 15 matches.
Gold Coast winger Indie, who wasn't in her Gold Coast side in the round-one loss to Sydney Roosters, is on a 10-game undefeated streak.
Jack has the NRL preliminary final to play against the Sydney Roosters on Friday night at Suncorp Stadium before Indie takes on Brisbane two days later at home in her NRLW prelim.
"I'm glad he is playing first so if he breaks (the winning sequence) then there is no pressure on me at all," Indie grinned.
"I like that we are winners in the family but I am trying not to think too much about it because it is going to start getting competitive."
Get through those games with wins and they will both be playing on grand final day together in Sydney.
"That would be pretty special for the family," Jack said.
"We are both very supportive of each other and both want to see each other there on grand final day."
The siblings' father Josh Bostock played on the wing for the Balmain Tigers and is a huge supporter. He was in Auckland to watch Jack win his first-ever final 26-16 over the Warriors.
There is an in-joke on social media in the family where the parents are taking the credit for the duo's feats.
"My dad takes most of the credit for it," Indie said.
"My mum grew up a netballer so she can't really say much. Dad likes to say he has some super gene."
There is another winning subplot also looming as Dolphins winger Tevita Naufahu, the partner of Indie, will play in the Queensland Cup grand final for Redcliffe Dolphins against Sunshine Coast on Saturday.
If Naufahu wins then he will play in the NRL State Challenge final on grand final day in Sydney.
"That would be really sick if that did happen. Hopefully it does," Indie said.
"I have no doubt in any of us that we will make it there but that will be a good day for the family."
Indie, just 19, left St George Illawarra at the end of last season without a contract but she has thrived at the Titans, scoring eight tries in 10 matches.
"It has been super exciting. I've loved it this year," she said.
"I came here not knowing what would happen but I have put in the work and I am grateful I am in the team."
Jack, 23, has enjoyed a stellar season, making his NSW debut in the winning State of Origin decider and named in Australia's 40-man initial squad for the World Cup.
Off-contract at the end of next season, Bostock has indicated he will re-sign with the Dolphins after the grand final.
"I want to stay," he said.
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