There are only two  reciprocal pronouns each other  and  one another . The reciprocal  pronouns are used to express a relationship in which the same thing is done by each of  two parties towards the other or more parties towards others. For example, Jack is  smiling at Jill and Jill is smiling at Jack. This is the same as Jack and Jill are smiling  at  each other . The smile is reciprocated by the other. 

The reciprocal pronouns refer mostly to people, but they can also be applied to animals  or things.  Each other  is usually used when writing or speaking about two people or  things. For more than two people or things,  one another  is generally used, but it is not  a rule that must be strictly followed. 

A reciprocal pronoun is used to shorten a long sentence by not repeating the same  action done by two or more people.

Examples:

  • Ray is waving to Roy and Roy is waving to Ray.
    Ray and Roy are waving to each other.

The subject has to be plural for the reciprocal pronouns to be used

Examples:

  • The  twin brothers  often argue with  each other .
  • Adam and Eve  have been writing to  each other  for years.
  • The  few puppies  chased  one another  across the field.
  • At the meeting,  they  insulted  one another

Reciprocal pronouns can be objects of verb

Examples:

  • This is the tenth year that you and I have known  each other . .
  • Before they began talking, they bowed to  one another . .

Reciprocal pronoun following preposition 

Examples:

The prepositions used here are at and with .

  • No one knows why they are shouting  at   each other .
  • They realized it would be much easier if they all cooperated  with   one another .

Reciprocal pronouns in possessive case.

Examples:

  • The couple whispered in  each other's  ears.   
  • The two old monkeys are seen scratching  each other's  heads.
  • When the two groups of delegates met, they started shaking  one another's  hands.
  • My girlfriend and I often visit  one another's  parents. .