How long do they normally live?
All else being equal, a Tened could expect to live for about the same amount of time as a human.
What was their society like?
Decentralized. While the various tribes/packs were in near constant communication with each other via the network of Perches, no one tribe could say that it ruled over others.
What sort of magic did they use?
Alchemy, healing, and necromancy were the schools of magic that they were the most skilled in.
Did they have writing and art? If so, what forms did they prefer?
Yes and yes. Their favorite form of artistic composition was the mosaic. Their works could be made from ceramic tiles, scraps of cloth, or even the arrangement of the written word. What mattered was many many small pieces of beauty and truth coming together to create an even greater expression of truth and beauty.
What was their religion like?
Eli was the only god they knew, but they did not worship Him like Followers or Rebuilders do. They did not sing songs of praise or make offerings at the altar. To them, worship was leading a just and good life. They gave praise to Eli not by singing hymns, but by striving towards an ever greater understanding of the world's secrets. Each tidbit of lore that they uncovered was an affirmation of Eli's magnificence.
What other types of creatures went extinct with them?
The most important animal in their day to day lives was the kharrakhaz(triceratops). The beasts were both vital draft animal and staple of the Tened diet.
Patriarchal? Matriarchal? Or something else?
The Tened were most certainly matriarchal both in the family and in tribal governance. The primary qualification to sit on a tribe's Brood Matron's Perch was to have hatched and raised no less than three clutches to adulthood.
Family size? Did they prefer big families, or did they prefer small ones?
An average clutch had two eggs. Females were fertile once a year in the late winter months. Incubation was approx 115 days. The Tened nuclear family amounted to the parents, their un-mated adult children, and juveniles.
Though females were only fertile once a year, Tened were sexually active throughout the year.
How long for children to wean?
Tened were dinosaurs, not mammals, so there was no milk for hatchlings to be weaned from. If you meant when the chicks transitioned from regurgitated food to solid, this usually happened when the child was four months old.