Claire chooses Frank for 20 years until his death and then she finds out
During An Echo in the Bone/Written in My Own Heart's Blood, Claire marries for the third time. This time it's to Lord John Grey.
The novel that launched the series, Outlander takes Claire back to 18th-century Scotland for the first time. On her time-traveling adventure, she meets Jamie. They marry each other in an attempt to save her from the clutches of Captain Randall, and fall deeply in love.
“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.
The day after their wedding, John gives Claire a large chest of medical equipment as a wedding present. Claire, remembering a similar anniversary gift Jamie had given to her a decade earlier, faints. A week after her marriage to Lord John, she and John drunkenly sleep together.
Grey falls in love with Jamie, who rejects his advances. Still, Grey cannot dismiss his feelings.
For instance, Lord John Grey learns the truth about Claire, Brianna, and Roger... though he has a hard time believing it.
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!
Jeremiah Alexander Ian Fraser MacKenzie, commonly called Jem or Jemmy, is the son of Brianna and Roger MacKenzie, and grandson of Claire and Jamie Fraser.
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.
Claire chooses Frank for 20 years until his death and then she finds out Jamie survived Culloden. She heads back to the past to choose Jamie for a second time. There's no way Claire and Jamie will choose someone other than themselves after this. They are endgame, and it doesn't matter what anyone else thinks.
Although Claire was disgusted by Dougal's proposition, she knew being a widow put her in a precarious position with no one to protect her against Black Jack. Claire reluctantly agreed to marry Dougal only if Jamie was already dead and her mission to rescue him from Wentworth Prison ultimately failed.
Jamie did remain faithful to Claire. It didn't stop him from being aroused. However, it just made him miss and want Claire more. Even in their 50s, the two are ready to be with each other sexually.
So, technically, Claire has three husbands in the Outlander books.
Jamie also has two stepdaughters, Marsali MacKimmie Fraser and Joan MacKimmie, from his marriage to his second wife, Laoghaire MacKenzie.
Sadly, William's birth resulted in the death of his mother Geneva and as Jamie was unable to step up given his position at the house, Lord John Grey agreed to raise William as his own.
The simple answer is no. Claire and Jamie don't have any more children after Brianna.
To recap: By Gabaldon's timeline, Jamie and Claire's age difference is 5.5 years, while on the show, that age gap shrinks to 4.5 years.
They settle in 20th century Lallybroch, following along somewhat with what Claire and Jamie are up to in the 18th century by reading a series of letters from Claire to Jamie.
It reveals a strange birth mark, which Roger says he also has. The moment seems to confirm Roger is Jemmy's biological father, rather than the rapist Stephen Bonnet. The finale ends on the cliffhanger of Claire and Jamie being separated while she is imprisoned awaiting trial.
In September 1764, Lord John told Jamie he intended to marry Isobel Dunsany and become William's stepfather. Jamie offered his body to Lord John, who declined. Jamie kissed him.
Brianna ends up asking John to marry her as a way of avoiding being proposed to by a total stranger, which—actually, scratch that. Brianna threatens to out John as gay if he doesn't marry her, he gets understandably pissed, she apologizes, and he eventually agrees to the engagement after a brief bonding session.
His descendants–a few of whom he meets now and then in his travels–have the blue light about them, too; in large degree or small, depending on their talents. So he knows Claire, when he sees her, as one of his great-great, etc. grand-daughters.