Thomas Peterson, 16, also says Drew is the "greatest dad in the world."
Thomas, his 14-year-old brother, Kristopher, and Drew appeared on The Early Show Friday, along with the lawyer representing Savio's family, John Q. Kelly.
The suit, filed on behalf of Savio's estate, claims Peterson, a former Bolingbrook, Ill. police sergeant, drowned Savio in her bathtub in 2004.
Savio's family has long voiced suspicions about the circumstances surrounding her 2004 death, especially following the disappearance of Peterson's fourth wife, Stacy, in October 2007.
Peterson has been named a suspect in Stacy's disappearance, but hasn't been charged. Authorities haven't identified him as a suspect in Savio's death.
Peterson has denied any involvement in either case, and his attorney, Joel Brodsky, this week reiterated Peterson's innocence.
Savio's death, initially classified as an accidental drowning, was reclassified as a homicide after her body was exhumed and another autopsy conducted following Stacy Peterson's disappearance.
The lawsuit, filed by Savio's father and sister, was widely expected. Many of the allegations in it have been reported in the media since Stacy Peterson vanished.
The suit, filed in Will County, Ill., seeks more than $100,000 and alleges Peterson killed Savio before a scheduled trial over the divorced couple's property.
But Kelly told Early Show co-anchor Julie Chen Savio's father, Henry Savio, and sister, Anna Doman, don't stand to gain "one penny from the suit. "They have no financial interest in the lawsuit whatsoever. It's only for the estate and Kathleen's two minor children."
If the suit succeeds, Kelly explained, "All the assets that should have gone to the children originally, all the marital assets and things like that, would be properly segregated for the children. And Mr. Peterson would be taken to task and labeled for what he had done, causing (Savio's) death."
Peterson was given control over various assets "to use at his discretion, rather than segregate it to his children," Kelly noted.
Thomas Peterson told Chen he thinks the suit is "ridiculous. Because what they're trying to do, they're trying to take money from my dad and basically give it back to us. Now, do the math. He's got everything put into us as it is. So it just doesn't make sense to me."
Thomas says he doesn't remember ever even meeting his grandfather, Henry Savio, and hasn't seen his aunt, Doman, in six years, adding, "They've made no attempt of contacting me. So I haven't really seen them."
He also came to the defense of his father, saying, "Accidents happen all the time" and "I highly do not believe that my dad had murdered my mom. Because, first off, he wasn't there, he was with us during that period of time. I don't know what else to say. I don't believe it."
Thomas and Kristopher live with Drew, and Thomas says the intense media focus on Drew has been difficult to deal with: "It's been crazy, like, with the news media in front of my house all the time. And like, there really hasn't been much of an impact ever since my mom died, because nothing could be worse than that. But it's just made my childhood much harder."
As are, he said, suggestions that Drew killed Savio. "That's just making it even worse," Thomas remarked. "I'm seeing a lot of the world and a lot of the people's true motives."
What does he want to say to the public about his father?
"I would say that he's the greatest dad in the world. Not a lot of people know that. People see the news all the time and what everyone has portrayed him to be. But to our family -- no one could ask for a better dad."
Drew Peterson told Chen a woman who claimed at one point to be engaged to become his fifth wife no longer lives with him.
And Kelly, the lawyer for the Savios, added, "By all accounts these young men loved their mother. Their mother loved them. To see them thrust on national television to talk about her untimely death right now is unsettling, too."
He also noted that the family will probably wait for the results of a grand jury probe of Savio's death before pursuing the suit any further.