How to map sales team to all my contact
Do I understand the intention here, ie John has relationship to Mary, Bob, Harry, then on an Event registration page automatically fill the form with Mary and/or Bob and/or Harry (as well as John or not?).

There won't be any way to do this out of the box in civicrm afaik. Since you are on Drupal you are more likely to be able to get close.

John can go to a form and use an autocomplete/dropdown to find contacts he has 'permission' to see, which you can provide by making your Relationship between John and the others Permissioned (see this Extension if you want to make those types of relationships always permissions)

You can then set up the webform to allow John to add multiple of his sales team, or probably have them all load automatically

And yes the Webform-civicrm can be used to add these contacts to an Event, and accept payment depending on the type of payment processor you use.

Webform_civicrm is very well documented so i would suggest you read, try and come back with more detailed questions