HOW TO CREATED a RELATIONSHIP BETWEEN 2 or More CONTACT

HOW TO CREATED a RELATIONSHIP BETWEEN 2 or More CONTACT

Hello Everyone, 
I am trying to trouble shooting the creation of a Relationship between 2 or more Contact, that is not related to a hierarchy or based on an organization. 

We are in the travel business and we need to create a relationship between 2 or more Contacts that may travel Together ( one time) , or are Family Members , so that each INDIVIDUAL CONTACT record remain independent and can include all the specific information of such Contact, but can show the relationship with one or more contact related. (ie a Referral, Family Member, Friend , Travel Companion, Spouse etc). 

Anybody can help suggesting the best way ? 

Thank you

Tommaso De Poi
TRIPS 2 ITALY,LLC