Hello ElCid
I'm an English learner from Japan. I know I myself am not good at English. But if you don't mind, I'd like to try to answer your question. Maybe I'll make many mistakes in the answer, but I'm sure in this case our teachers come to correct them. So please allow me to do my try. OK?
| 1) Say the same thing twice over. |
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I agree with you that this 'over' has almost no sense. But 'twice over' seems a collocation often used. (EX) He read my typescript twice over. (EX) They painted the wall in white thrice over.
| 2) I know him best or I know him well. I know him very well. |
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'I know him well' means 'I am well acquainted with him' but sometimes it means 'I and he have a special relation (= be in love)'. I don't know much about the phrase 'I know him best'. I feel your mother or your husband/wife might say 'I know him best'. But I think, in cases other than that, people would rarely say 'I know him best'.
| 3) Is there no later news than last week? |
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I feel this sentence is grammatically wrong, but I can't explain the reason well. I would say in this case rather: 'Have you got any news since last week?'
| 4)Elder is used only of persons. |
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This 'of X' can be paraphrased as 'concerning X', 'about X', 'with regard to X' or 'in reference to X'. As I'm an English learner, it's not easy for me to explain this kind of usage of 'of'. But please think about the phrases like 'think of X', 'consider of X', 'talk of X', 'hear of X', and 'speak of X'. In these phrases, the verb is intransitive, nevertheless 'V(=verb) of' functions as a transitive phrasal verb and X works as the direct object of 'V of'.
paco