1 claiming they are doing ancestry testing是做people的后置定语,比如people sitting in the bedroom,这都是类似的.声称他们正在做实验的人.
2 whom to compare DNA with,这样看是不是清楚点?with whom to compare DNA是一个定语从句,修饰先行词candiate候选人.compare with 是个词组,意为与某个比较,whom是宾格,因为用在介词with 后要用宾格,所以不用who （只能作主语）.
3 which 前有“,”,是非限制性定语从句,都是指代整个句子,没有“,”的定语从句是前面名词的定语从句,修饰名词.