Yes, quite easy. Add an author_id integer column to your Event
model, then update your code as follows:
class Event < ActiveRecord::Base
has_many :events_staffs, dependent: :destroy
has_many :staffs, through: :events_staffs
belongs_to :author, class_name: 'Staff'
end
As for members, I'd create another join table similar to your staffs_events table, but for members. Within that model you'd need to do the same belongs_to association as with Event where you specify the class_name for the member.