Don't feel it's your decision to make. Spare yourself that burden. Support your family's decision, whatever it is.
Be strong for him, hold yourself together and treasure the good times you've had. Carry all the happy memories with you. Try to make sure you have photos or videos for the future.
Have you been to see him in hospital? If not, think twice about doing so. You could find it very upsetting and unhelpful in the current circumstances.
Hope for the best but prepare for the worst. Good luck ...