5
This しなければなりません just means "must", "need to", "have to". And that's the only meaning of しなければなりません.
この会に来たインドの人は「日本にいろいろ教えてもらって、早く空気をきれいにしなければなりません」と話していました。
An Indian person who came to the meeting said, "[I] have to make the air (of India) clean after Japan taught a lot of things to [me]."
An Indian person who came to the meeting said, "[We ...
3
You don't really have to do anything special- just put the final verb (adjective) in the past tense.
学校まで走らなければならない - I have to run to school
学校まで走らなければならなかった - I had to run to school
This works with all three of the constructions you mentioned.
ならない = ならなかった
だめ(だ) = だめだった
いけない = いけなかった
Of these, I see ならなかった the most by far, but the other two ...
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