Do ear drops ever reach the eustachian tubes? I have what we thought was an ear infection that ended up being a sinus infection.<enter dizziness wow!

Should not. Drops into the external ear canal will not reach the eustachian tubes unless the tympanic membrane (ear drum) is perforated. It is not uncommon for a person with an upper respiratory infection to have it affect the sinuses, middle ear, and so on.
All connected. The eustachian tubes empty into the oral cavity and the oral/nasal cavity is connected to the sinuses, so it's all one interconnected space. If thengs get blocked up it is not uncommon to have ears and sinuses both affected, either simultaneously or sequentially.