HIGH LIFE: A WEEKLY FORUM FOR HIGH SCHOOL STUDENTS : The Keys to Sibling Harmony : Pianists: Sisters Jinah and Jin Yoo of Sunny Hills High School push each other and offer support.

Sibling rivalry can take unexpected twists. The often-destructive emotion has helped make two Buena Park sisters into excellent musicians.

Jinah Yoo, 16, and Jin Yoo, 14, students at Sunny Hills High School in Fullerton, have pushed each other for years. Jinah has been playing the piano for 10 years, and Jin took up the instrument seven years ago after seeing her older sister play.

“My sister had some effect on my playing the piano,” Jin acknowledges. But even though she’s grateful that her sister got her interested in music, Jin thinks Jinah should thank her for not letting Jinah quit.

Jin said, “She wanted to be better than I was, so she had to keep playing.”

To up the ante, Jinah started learning the flute four years ago. “The older sister should be better than the younger sister, and I am older,” Jinah said. Jin, in turn, took up the violin.

The rivalry extends to formal competitions.

“When we are competing, we always support each other by accompanying each other with our separate instruments,” Jinah said. “But when Jin wins a competition, it makes me mad and frustrated because it proves that she is better than I am.”

If Jinah and Jin sometimes lag in their mutual support, their parents, Byung Hak and Soon Hee, are there for them always. They bought each girl a grand piano and make sure the girls practice daily. But things are not as equal as they seem: Jinah practices two hours a day, and Jinah puts in three.

Their competitiveness has paid off in numerous awards. Jinah was selected the Senior Baroque Winner of 1992 and 1993 by the Music Teachers Assn. of California. She also won first place in the Long Beach Mozart Festival in 1991, the 1989 Southwestern Youth Music Festival in Dominguez Hills and second place in the Southwestern Festival in 1990.

Jinah also won honorable mention from the Music Teachers Assn. in the California Bach Festival and Greig Competition in 1990. With her flute, she took third place in August at the Southwestern Festival.

Jin in January took top honors at the state Bartok Competition sponsored in Sacramento by the California Assn. of Professional Music Teachers. She also won the grand prize in the 1990 Long Beach Mozart Festival and has placed first three times in the Southwestern Festival.

Jin once beat Jinah in the Long Beach Mozart Festival; Jinah went the following year and won in her division. But the catch is that Jin did not compete that year.

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As do all musicians, the two have their favorite pieces--but not the same ones. Jin favors Mendelssohn’s “Duetto,” Gershwin’s “Preludes,” Chopin’s “Fantaisie Impromptu” and Debussy’s “Suite Burgamasque”.

On piano, Jinah works on pieces by Haydn, Brahms’ “Balladens” and “A Walk in Spring” by Roy Harris. On flute, Jinah enjoys sonatas by Handel and Mozart and “Last Frost and Spring Shows Her Colors” by Kathlyn Maine.

The girls don’t hesitate to say what they don’t like, either.

“I dislike Chopin’s ‘Etudes,’ ” said Jin. Jinah says she hates many contemporary pieces that have too much dissonance. And she dislikes having to use the piano’s black keys. “The sharps and flats make the music pieces hard to read,” Jinah said. “I tend to quit on things I don’t like.”

Jinah can reach up to nine keys with one hand, but Jin can reach 10 keys.

“Jin is always better than I am in anything,” Jinah pouted, “whether it is academics or music.” But Jin countered by saying that Jinah is more social.

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When the two are not competing, their schedules are full. Both are in honors classes, are involved in California Scholarship Federation and volunteer for the Red Cross. They also study jazz and ballet.

Each Saturday they sing with the Korean American Youth Choir of California in Los Angeles. The two plan to go on tour in Korea this summer with this group.

The sisters say they are always together. “Jinah acts like my mom, and she always looks after me,” Jin said.

They share not only the same interests but also the same clothes. “Sometimes Jinah gets possessive and says ‘your clothes’ and ‘my clothes,’ ” Jin said.

The two agreed music will always be part of their lives. Neither girl, however, has specific plans to make it a career.

“I just hope (music) is a part of my life I can just enjoy. I really want to go into business,” Jinah said. Jin is even more blunt: “I have no future plans. I’ll play it by ear.”