He's Linda Lavin's tall and toothily handsome son on CBS' long-running sitcom Alice. She's the tough-talking, street-smart Jo on NBC's comedy-melodrama for the Clearasil set, The Facts of Life. Together, Philip and Nancy McKeon, at 17 and 15 respectively, add up to more than the sum of their parts. Now that the Osmonds have sundered and the McNichols diverged, they are TV's new dream teen siblings. No one is more startled at the turn of events than their parents. "If anyone had told me 10 years ago, when I was a travel agent in New York, that the kids would bring me to this, I would have laughed," says their father, Don, who now co-manages his children's careers. More remarkably, despite a combined paycheck well into six figures, Philip and Nancy both seem like normal—though dissimilar—all-American overachievers.

Older brother has the lighter heart. "I joke a lot—everything is funny to me," shrugs Philip, who literally grew up during his five years on Alice—from 4'11" to his current 6'2" and still climbing. "I was treated like the kid on the set at first," he observes, "but that was okay—after all, I was the kid." His TV character has grown up even faster. "On the show, I've quit school, left home, fallen in love with an older woman—things American kids do all the time," Philip deadpans. "Mind you, I haven't robbed any banks yet." His own home life has been more conservative. "It's not that I couldn't go out or had to eat all my vegetables," says Philip. "My parents are pretty laid back, but if I said, 'Folks, I'm taking off for Vegas for a couple of days,' I think they might have something to say about it."

Nancy, in contrast, sees herself as "a very serious kind of person, maybe too serious." Before signing on with Facts when she was 13, she gave the producers her strong opinions on her motorcycle-loving character's development. "Jo originally was a lot like the Fonz; then they wanted to take away some of her dominance, which I didn't want to do," Nancy recalls. "So we talked about it, and came up with the way she is now. She's not the Fonz, she's not a wimp; she stands out alone." That's a trait Nancy admires. She bluntly labels films like Endless Love and The Blue Lagoon "exploitative," and as for drugs, "I have more important things to do with my time," she says. "That's why I like Jo: She doesn't bow to peer pressure and thinks anyone who does is a nerd."

The McKeon kids are close, with no hint of rivalry. Perhaps one reason is that both have been working for years. Nancy began modeling baby clothes for Sears catalogs at age 2; Philip was out of work until 4. "I must have been an ugly baby," he figures. His first commercial was for Fruit Loops; pretty soon their dad and mom, Barbara, then a housewife and now a nurse, were shuttling them from Forest Hills, Long Island to Manhattan for what would be some 60-odd commercials in seven years. Their parents encouraged a seriousness of purpose. "They figured if you decided to take singing and dancing lessons, you should practice—but there's been absolutely no pressure," adds Nancy. "Mom and Dad have always asked us every step of the way if this is what we wanted to do."

Family life changed radically when Philip landed Alice in 1976 and the McKeons decided to go West. "I was happy for Philip, but I had to start all over again," says Nancy. "I was getting up at quarter to 5, practicing singing and dancing before school and again when I came home, but nothing was happening. I thought of quitting." After three years of auditions—and numerous brotherly pep talks—she began landing series guest spots and eventually The Facts of Life.

Both study with tutors three hours a day on-set (they have A averages), attend Catholic Mass every Sunday, date ("no one anybody's ever heard of," says Philip), and go to the flicks together (they walked out of the sexy Body Heat in embarrassment). "I eat hamburgers, Cokes and fries and play tennis," says Philip. "How much more normal can you get?"

Well, maybe a little. It isn't every 17-year-old who drives a 1981 Cadillac Coupe de Ville and, Nancy tattles, listens to morning stock reports on the radio. Nor can most teens help their family move from three bedrooms in middle-class Burbank to a five-bedroom, four-bath house in high-priced Hollywood Hills, as the McKeons will do soon. Probably even fewer kids spend so much time planning their futures. Philip wants to learn to direct and to cut an album as a pop singer. Nancy wants to make feature films and already has precociously optioned a family novel called Starring Peter and Leigh for a TV movie. Filming begins this spring and she will star.

More than anything, they'd like to work together. "That's a constant dream we have," says Philip, adding proudly, "Nancy is one of the best actresses in the world." Not to be outdone, Nancy responds, "I think he'll become one of the finest directors of our time. If I had to pick a brother," she adds, "I'd pick him."