Scientists are amazed that a human could have either,let alone both,of these qualities.Althouh Zalmer sees himself as"just a regular guy",he once rescued a family from a house on fire after the firemen had given up.
科学家们非常惊讶一个人可以具有这么多（优秀）品质,更不用说是两种了.尽管Zalmer一直认为自己“只是一个平常人”,但他曾经在消防员放弃之后从一个失火的房子中救出了一家人.
说实话不知道全文又是什么内容,所以对你后来补充的句子理解得可能有点偏差,但从语法意思来讲应该是对的.Scientists are amazed that a human could have either,let alone both,of these qualities.其实后两句顺序被换过来了,let alone是更不用说,遑论的意思.正常语序是Scientists are amazed that a human could have either of these qualities,let alone both.