Avoid duplicate opportunity records created by each member of a sales team. Instead, create an Opportunity Team so that all the members of a team can access the same record.
Setup > Customize > Opportunity > Opportunity Teams > Settings
Select check-box to enable Team Selling and save.
Select Opportunity Page Layout for which you want to opportunity team as related list.
When Opportunity Teams is enabled following options you can add custom fields, buttons, and links, validation rules, and Apex triggers to opportunity teams.