YOU SAID:

the dog, called Jeff, plays the piano while singing

INTO JAPANESE

ジェフと呼ばれる犬は歌いながらピアノを弾きます

BACK INTO ENGLISH

A dog called Jeff plays the piano while singing

INTO JAPANESE

ジェフという犬が歌いながらピアノを弾く

BACK INTO ENGLISH

A dog named Jeff sings and plays the piano

INTO JAPANESE

ジェフという犬が歌ってピアノを弾く

BACK INTO ENGLISH

A dog named Jeff sings and plays the piano