Copyright of translated articles and books

Copyright contains many rights. If you only buy the right to translate, you can only translate and not tamper with the original text. Of course, if translation is needed, it can be modified appropriately, provided that the author agrees. So you said you bought the copyright. What part of the copyright did you buy?

For the first question, I feel that I only need the author's consent, and I don't need to ask the translator's consent first.

The second problem is that a work without copyright does not mean that it is not copyrighted, but at most it is not registered, so the first translator does not own its copyright.

The third question also involves the specific part of copyright. If you are not granted the right to publish, of course, public publication is illegal. As for plagiarism, you are only a translator, not the original author. It should be normal for most of the contents to be consistent.