他的双亲，是his both parents还是both of his parents

his parents和both of his parents都行。both在这里是重复的。。。除非要强调是两个人都……不强调时建议省略，避免重复语法错误。

his parents就可以了，非要加一个both 的话,就是
both his parents....

是后者，因为英文是不能以中文的顺序直说的，那会被老外笑话的

his parents就可以了，为什么非要加一个both……