Submit a webform as soon as you can and wait for them to reply. You might not get a refund but you can certainly withdraw your application and reapply.
I believe you can add them to your application instead of withdrawing your current application and losing your place in line. Please call IRCC on their helpline and discuss your options with them. Good luck!
I dont think you should withdraw your application, call IRCC to explain your situation & they might give you a solution to add your family members -
1 (888) 242-2100
To speak to an agent, dial 3-4-1-0