Does the fast become invalid by a drop of water entering the ear during ghusl, when there is no certainty, and is it invalidated by a very small amount of blood exiting?

Ear drops do not break the fast. If they entered unintentionally, the fasting person's fast is not broken. Certainty is not dispelled by doubt, so the fast is valid. Also, the emission of blood does not break the fast, unless it is menstrual blood.