Does an external ear infection need to be treated wiht ear drops and with regular antibiotics together? Can we just use the drops?

Drops. The external ear infection should respond to topical antibiotics - ie. Ear drops.
Usually just drops. An uncomplicated external ear infection that does not extend outside the canal to the outer ear should initially be treated with just antibiotic drops. If the patient has a decreased ability to fight infection, as in diabetics and immunocompromised people, or when the infection extends beyond the ear canal, then oral antibiotics may be indicated.