House Durwell was a Reach house that went extinct 200 years before the series began.
Lord Garibald Tarwick questions Mira Forrester on Sera's last name, knowing the Durwells went extinct 200 years ago. Mira can either lie to Lord Tarwick, saying she's met them, they still exist but are small, or reveal that Sera is actually a bastard.
In the books
The Durwells are mentioned in the Tales of Dunk and Egg prequel novels, set about 90 years before the events of the main novels. House Durwell is mentioned in passing as a house from the Reach whose lands border that of House Webber. The Durwells were renowned livestock thieves.
The Telltale video game said that the Durwells went extinct 200 years ago, conflicting with their presence 90 years ago. Houses often have numerous cadet branches, however, and the Durwells that border the Webbers are only a minor House - it is possible that a larger main branch of the House went extinct some centuries ago.
Houses from the Reach
Durwell · Gardener