Active and Passive Voice

Raveena writes "The cake was bake by her", thinking adding "was" is enough to make a sentence passive. Her brother says the verb's form must change too. Who is right?

Converting "The dog bit the man" to passive, Samar writes "The dog was bitten by the man", thinking the word order stays the same. His teacher says who got bitten has been switched around. Who is right?

Ayush says "My bike was stolen" is an incorrect sentence, since passive voice must always state who did it with "by" — here "by someone" is missing. Is Ayush right?

Nikhat tries converting "He arrived at the station" to passive and writes "The station was arrived by him". Her brother says this sentence cannot be made passive at all. Is her brother right?