McStay said he knew a lot about his son's business because he was the initial investor in the company. He also said he knew his son had been to Mexico, or at least to the nearby border towns, late last year to pick up granite countertops for his home kitchen, which he was renovating.
"I don't want to say the words," McStay said when asked what he thought might have happened to his son, daughter-in-law and grandsons.
"This is one of the smartest young men you'll ever meet, he doesn't have a mean bone in his body," he said.
Michael McStay said of his brother, "He is not on a vacation. He wouldn't leave the dogs uncared for, and he's worked very hard to build his company up.
"He would not leave his business and not return e-mails or phone calls. It's an Internet-driven business," he said.
A voice mail box at the company's San Clemente, Calif., headquarters was full.
The outgoing message on the McStay's home answering machine is a chipper one, encouraging callers to "have a nice day."
"I just want my brother and my nephews and my sister-in-law back," Michael McStay said. "Those boys are adorable. We just want them all back."
McStay said he and his older brother, who is called Joey by those close to him, were best friends growing up in Texas.
"My brother is awesome," he said. "He is such a compassionate, caring person and so giving. He's likable and honest. That's why so many people are rattled by this."
Asked whether he could think of anyone who may have wanted to hurt his brother, McStay said he couldn't think of anyone who didn't like his brother.
Speaking on behalf of his parents, who he said are both "a wreck," McStay said that while he's praying for the family's safe return, he's not naive.
"With what's going on in today's economy and how close his car was found to the border, the first thing I'm thinking is that it has something to do with money," McStay said.
"People do stupid stuff for money, but I'm praying for the best."