These parts of Wikipedia are not very reliable. For first names, I would rather trust this site, but in the case of Nitin, I do not agree with this site either. First the Hindi spelling at this site spells it as नीतिन with a long ee (i.e. Neat-in, except the t is soft as in French tu), whereas the more common spelling नितिन has a short i (i.e., Nit-in, again with the soft t). Second, the last -n is not explained by the claimed meaning.
I think Nitin is originally a short form of some names beginning with nitya, e.g. nityAnanda. nitya is a Sanskrit word which originates in the particle ni that expresses the concept of within, into or back, and nitya means innate, but often expresses (even in the earliest uses in the Rigveda) the sense of basic or perpetual quality. Thus with Ananda (A- completely + nand please + a), it could mean someone who is permanently happy. The occasional long -ee- may come because the heavy consonantal cluster -ty- is simplified to a lighter -t-.
Sharma is the nominative word from the Sanskrit nominal root sharman, probably connected to the verbal root shri, ultimately cognate with English lean. sharman originally (e.g., in the Rigveda) meant shelter or protection, but slowly came to mean the simpler comfort or happiness. It was one of the primary qualities that was supposed to characterize brahmins, the highest caste, and was added to the names of people of that caste. Today, it is sometimes used as a last name, often among brahmins, but is also sometimes used as a name element.