Usage of "the" in sentences

[Bond007]

Is the needed in the following sentences? What does the sentences with and without the mean?

1. (The) people who stand by you in your tough times are the best friends of yours.

2. This notice is for (the) people who want to donate blood in the camp near the university ground.

3. (The) students who used to read at this school are very successful now.

4. Nikolas Maduro betrayed (the) people who voted for him.

Another question, please tell me is it necessary to use the ?

5. John: What do you think about nikolas maduro getting elected as president regularly after so much anarchism in Venezuela? Me:- I think the people have no choice other than him to vote for.

I think 'the' is necessary. what do you think?

As an ESL learner this kind of question bothers me a lot. it is still not clear to me. Can I have a broad discussion please so that I can understand the whole thing?