Describe the Tuck family.

The Tuck family is comprised of four individuals. Angus Tuck is the father, Mae Tuck is the mother, and the two sons are Miles and Jesse. I would probably say that the Tuck family's defining characteristic is that they are immortal. They were blessed/cursed with immortality after drinking from a special spring found in a forest near the Fosters' home.
Jesse Tuck is the youngest of the family, and he is also the most youthful in spirit. He is the only member of the family that still thinks being immortal is a great thing. He's 104 years old, with the physical and mental maturity of a teenager.
Miles Tuck is the older brother. He has been married and has had kids. Unfortunately, his immortality doesn't let him age, so his wife got scared and left with their kids:

"I was more'n forty by then," said Miles sadly. "I was married. I had two children. But, from the look of me, I was still twenty-two. My wife, she finally made up her mind I'd sold my soul to the Devil. She left me. She went away and she took the children with her."

Miles isn't as excited about immortality as Jesse is, and he sees major issues with being able to live forever. What's interesting about him is that his concerns are on a worldwide scale. He specifically mentions the potential issue of overpopulation if everybody were allowed to live forever.
Angus Tuck is definitely the Tuck family member that is the most bitter about being immortal. He strongly explains his position to Winnie by telling her that life without death isn't actually living:

You can't have living without dying. So you can't call it living, what we got. We just are, we just be, like rocks beside the road.

He's obviously a loving father and husband. The best evidence for this is that he and Mae are still happily married to each other.
As for Mae, she is patient, kind, loving, and protective of her family and of anybody that is willing to do right by her family. That's why she violently protects Winnie from the man in the yellow suit.