So do native English speakers. 'Whom' sounds very formal to the ear of native speakers. Lots of people would be just as confused as you. In normal writing and day to day speech it is not used. I wouldn't be surprised if in future it disappears from the language.
Anyway, you have written all the sentences correctly, with the exception of the first one.
a) TO whom did you give the book?
Interestingly, the structure using 'to whom' matches the structure in Spanish.