First I will answer your second question.
1)Why does translation defer from word-to-word pedantic translation ?
There can be a problem with your translation. I am not saying anything about translator because I don't know whose translation you quoted. Many times very great Sanskrit scholars can even do this mistake. But for your satisfaction, I am quoting ...
To the question "How can same upanishad be available in two shakas?" ,
There is no prohibition for a certain Vedic passage or verse, whether classified as Upanisad or not, to be part of different recensions. Vedic recensions are natural evolutions (or side effects) of oral (and aural) tradition by which the concepts were passed on through generations. From ...
If purusha, prakriti and parmeshwar are eternal, did god not create them?
He did not create Jivatmas or Prakriti (material elements) because they are both eternal, but he still created the universe, all its heavens, hells, underworlds, lifeforms, etc. by modifying Prakriti, and he put Jivatmas in those bodies based on their karma.
According to Vedanta, ...
Commentary of Shankaracharya on Nṛsiṃha pūrva tāpaniya Upanishat exists.
Collected Works of Sankara 1910 Edition published by Sri Vani Vilas Press, Sri Rangam.
This book is a collection of various works which are believed to be written by Adi Shankaracharya. It contains following works:
There are 108 Upanishads. See question here - Available sources for the 108 Upanishads?
I assume you are referring to the Nrisimhatapini Upanishad. Adi Shankara wrote commentaries on 10 Upanishads (possibly 11). Swami Nikhilananda writes in his 4 volume translation of the major Upanishads (The Upanishads: A New Translation, V1, General Introduction, p 9):