Hi,
The subjective case indicates that the word is a subject or a subject complement. eg: The proposal ignores many who (subject) need help. I don't know why "who" here is a subject? If we regard this word as a whole, which means what is its function in the whole sentence, not part of the sentence, then I think "the proposal" is a subject, "many who ..." is object. Well, that's my thought, hope you can tell me.
You could say that the complete object of 'ignores' is 'many who need help'. But 'who' is still the subject of the subordinate clause. It depends on whether you want to look at the sentence as a whole, or at parts of it.
The objective case generally indicates that the word is the object of a verb or preposition. eg: A colleague whom (object of verb) they respected let them (object of verb) down. Who can tell me what's the object of "whom"? 'Whom' does not have an object. 'Whom' is the object of 'respected'.
And what's the object of "them"? 'Them' does not have an object. 'Them' is the object of 'let . . down'.
Best wishes, Clive