Vishnu, from the Vedic angle, is different from Purusha and Narayana.
While Purusha is the Cosmic form of Reality as explained in the Purusha Suktha,Narayana is he principle that governs the Universe setting the principles,
Nara Ayana, Path to be Followed by Humans.
There is another explanation that one who sleeps in the Water, Nara meaning Water.
Vishnu is different from Purusha and Narayana.
The term Vishnu is from Jishnu in Sanskrit,meaning one that suppots.
Vishnu is the Protector and His wife is Bhuma Devi, the Earth.
Vishnu was the One who has allowed King Bruthu to plough the Eart,.
Hence the name Prihvi for Earth.
Gaudiya Vaishnavam, there is a view that there are three aspects of Vishnus, or three Vishnus.
The Supreme God is Maha Vishnu.
This is represented by the Mahat Tatva of Sankhya.
Sankhya elaborates the Principles of Evolution, Starting from Mahat to Purusha, Prakriti,Ahamkaara,Three Gunas,Buddhi,Five Tanmatras, Five Elements,Five Organs of action, Five organs of Knowledge.
Ther form of Vishnu is Garbhodakaśāyī Vishnu.
This form is in the form of Creation of the Universe.
The third, Kṣīrodakaśāyī Vishnu, is diffused as the all-pervading Supersoul in all the universes in heart of every living being and is known as Paramātmā. He is present even within the atoms. Real object of meditation in Yoga is a Paramātmā. Anyone who knows them can be liberated from material entanglement..