YOU SAID:

they are not partial to themselves

INTO JAPANESE

彼らは自分自身に偏っていない

BACK INTO ENGLISH

they are not biased against themselves

INTO JAPANESE

彼らは自分自身に対して偏見を持っていません

BACK INTO ENGLISH

they have no prejudice against themselves

INTO JAPANESE

彼らは自分たちに対して何の偏見も持っていない

BACK INTO ENGLISH

they have no prejudice against themselves