Brianna and Roger do eventually go back through the stones, but it happens much later, in the sixth book, A Breath of Snow and Ashes. And their incentive for doing so is much greater than the half-hearted attempt we all just witnessed.
Book spoilers ahead.
Although Outlander series author Diana Gabaldon wrote "Journeycake," this plot of Roger, Bree, and Jemmy making a failed attempt to get back was not in the books. Bree and Roger do eventually go back to their own time in the Outlander novels after Brianna gives birth to their daughter Mandy.
By the end of book 6, Brianna and Roger, after the birth of their second child, decide to return to the future, taking Jemmy with them in order to escape the hardships of the 1770s; a storyline that would shake up Brianna and Roger's arc in the Outlander series for the first time since they came to the past in season 4 ...
The only storyline in the books that can be linked to Brianna and Roger, precisely in the 70s and 80s, is the one that sees them go back to the future to save their daughter, Amanda MacKenzie, born with a heart condition that would have killed her in the past, and that sees them move to Lallybroch.
In Outlander season 5, Bree and Roger settle at Fraser's Ridge with their son Jemmy. While it's believed that Jemmy can travel through time like his parents, when Bree, Roger, and Jemmy attempt to travel back through the stones to the 20th century in the Outlander season 5 finale, the stones refuse them passage.
Written in My Own Heart's Blood
On October 30, 1980, Jemmy is being held by Rob Cameron, who wants the boy to show him where Jemmy's grandfather has hidden gold.
She previously told one fan, who hoped for Jamie to time travel in the 10th and final novel: “Sorry, not happening.” Nonetheless, Jamie does have some powers after he was able to project himself into the future and appeared in Inverness with Frank Randall (Tobias Menzies) spotting him.
Following the Battle of Culloden, Fergus continues to live at Lallybroch, and Jenny Murray tutors him with the rest of her children. He sometimes brings food to Jamie, who lives in a cave near the estate.
When Jemmy holds the stone, it feels incredibly hot. It's so hot, it breaks in his hands. The stone is hot to the touch for Claire, Bree, and Roger, too. It's cold when Ian or Jamie hold it.
Either way, he eventually returns to Brianna and pledges his loyalty to her and their son, Jeremiah (nickname Jemmy). Bree and Roger are then officially wed during a Scottish gathering at River Run.
Roger is the father of Bree's baby in Outlander
After cutting Jemmy's hair to get rid of the lice, Bree saw a mole. She worried at first, but Roger was able to calm the fears.
Apparently, the stones realized that Brianna and Roger weren't ready to leave the 18th century just yet. They both said they'd wished to go "home" as the stones whisked them away, and that's exactly where they went: the place they now consider to be home, back with Jamie and Claire.
These stones come into play time and again on Outlander: Claire travels through the stones at Craigh na Dun in 1746 when Jamie brings her back to them in order to keep their baby safe, and then one more time in 1968 when she travels back to be reunited with her one, true love in 1766.
When Brianna travels to 18th-century Scotland, she marries Roger MacKenzie. They have a son, Jeremiah "Jemmy" Fraser MacKenzie, and a daughter, Amanda MacKenzie.
The simple answer is no. Claire and Jamie don't have any more children after Brianna. Claire heads through the stones while pregnant with Brianna at the end of the second season/book. She spends 20 years in the 20th century, and she and Frank don't have any children together.
First published and released in the United States on September 22, 2009, the novel continues the adventures of Claire and Jamie in the 18th century, as well as their daughter, Brianna MacKenzie and her husband, Roger MacKenzie, who returned to the 20th century at the end of the previous book, A Breath of Snow and Ashes ...
See, before her wedding, Jocasta signed over ownership of River Run to baby Jemmy so that Duncan Innes wouldn't have any claim to it; Jocasta was the estate's guardian until Jemmy came of age.
In the book, Jemmy's head is shaved after he gets lice, revealing a unique birthmark on his scalp. Claire Fraser (Caitriona Balfe) confirms this is genetic, which leads Roger to shave his head as well. He has the same birthmark on his head, confirming Jemmy is actually his biological son.
Well, at least until Bonnet wants to seal their agreement with a kiss, at which point he realizes Brianna has no real feelings for him. Unfortunately, he reacts in the worst way possible: by forcing Brianna to watch him have sex with a prostitute, and then selling Bree to a business associate for six pounds.
Because yes, Claire and Lord John end up married in book seven, and yes, they drunkenly (and full of grief for the loss of Jamie, whom they both love with all of their heart) consummate that marriage. And then Jamie shows up alive and well!
It's possible that Amelie's sister is the one who gives birth to the line that leads to Claire. Fergus will still be an ancestor but not a direct ancestor and that would mean Laoghaire isn't one of Claire's ancestor.
A Breath of Snow and Ashes
Henri-Christian is born as the fourth child of Fergus and Marsali. He is a dwarf and some of the residents of Fraser's Ridge believe he is a punishment for his parents' sins.
“He's about 25,” Gabaldon said. It's an interesting response. If you're up to date on the series, then you know that Jamie is not dead at the age of 25.
Claire asks Lord John if he believes she (and Brianna and Roger) are from the future, to which he says that he doesn't, but that he will behave for all appearances as though he does.
“I curse you. I curse you with knowledge, Jack Randall. I give you the hour of your death. Jonathan Wolverton Randall, Born Sept 3rd, 1705, dies…” she whispers in his ear, and suddenly he knows that she's telling him the truth.