We can't help but feel bad for Denise, Billy's mom. She's one of those people who has been beaten down for so long that they're hardly capable of standing up for themselves anymore. Since Ray is such an insufferable jerk, she gets her tiny little paybacks by acting absentminded whenever he needs help. But those miniscule, passive-aggressive acts are all she ever does:
Denise waited on her husband's every need, though she was never quick about it, Billy noticed, she seemed quite fine with him harrumphing a second and third time, and when she did get around to fetching, pouring, cutting, she performed with a multitasky air of distractedness, like she was watering plants while talking on the phone. She was sneaky. She had those passive-aggressive wiles. Her hair was an indeterminate washed-out chemical color, and most of the emotional muscle tone was gone from her face, though she was still capable of sad, skewed smiles from time to time, forcing the cheer like Christmas lights in the poor part of town. She strove mightily to keep the conversation upbeat, but family troubles kept leaking in around the edges. Money troubles, insurance troubles, medical-bureaucracy troubles, Ray-being-a-stubborn-pain-in-the-ass troubles. (Bully.21)
Denise even feels compelled to talk to Ray's mistress whenever she calls to ask for money, because heaven forbid Denise could be rude to the lady. Denise's door-mat-ness drives her children crazy, but Denise herself goes on, mostly oblivious to her kids' distress. She's a character you just have to feel sorry for—and that helps us understand Billy's drive to try and help her even more.
Kathryn, Billy's sister, was the most promising of the Lynn kids. Billy sums her up like this:
[…] Kathryn, his middle sister and the star of the family, an extremely beautiful girl and gentle and smart who won a partial scholarship to TCU. So far so good. Majors in business, joins a sorority, makes dean's list every term. All good. Becomes engaged to a guy three years her senior who's getting his MBA, kind of a tight-ass pussy boy and far too impressed with himself, but it's still good, mostly, sort of, even though Billy secretly hates the guy. (Private.41)
But then Kathryn got into a nasty car accident, leaving her face severely wounded. Her fiancé, the aforementioned guy decided that he couldn't handle her injuries, so he dumped her. This is what led to Billy's fateful decision to trash the "tight-ass pussy boy's" brand new car and then run after him with the crowbar he'd used on the vehicle.
That little act of revenge is why Billy got strong-armed into the joining Army: he had to do it to avoid jail time.
The whole episode has led Kathryn down a pretty different path, leaving her stranded at home to get more and more bitter and frustrated with her lot in life. In addition, she feels like it's all her fault that Billy is getting re-deployed to Iraq, and it's this guilt that makes her reach out to the lawyers in Austin who work to help soldiers go AWOL as a statement against Stop-Loss.
Even though she's clearly trying to help Billy, Kathryn unknowingly presents him with the difficult challenge of deciding whether or not going back to Iraq with Bravo is the right thing to do.
Patty, Billy's older sister, is also the oldest of the Lynn children. She went from being a teenage wild child to a young mom who seems to be trying to get her stuff together. She's mother to Brian, the little nephew who charms Billy when Billy's home on leave.
Pete, Patty's husband, is married to Billy's older sister, Patty. He works oil rigs around Amarillo.