You narrate to them a Hadith; 'that all sons and daugters of Aadam make mistakes and the best amongst them are those who seek forgiveness and forgive'.
And say to them Allah is forgiving so why cant you be forgiving.
and if it still dont work then get down on your knees and beg for forgiveness till they forgive you.
and another thing would be to say sorry and if they have a heart of Gold they will forgive you.
and the last resort would be to give em a slap in the face and tell em to wake up to reality and tell em that everyone makes mistakes and they should learn to forgive and forget.