How do I properly cite a research paper?
Why not both?
"As summarized in \cite{A}, both \cite{B} and \cite{C} equally
contributed to the discovery of $FancyResult."
"Smith et al discussed a new approach in \cite{X}. While the result is not yet complete (see \cite{X1,X2,X3} for work on it and \cite{Y1,Y2} for critiques), it contains interesting aspects that shouldn't be overlooked."
It is usually not a problem to use the same word as an author, especially if it is a technical or predefined term. Especially if you mention the source in the same paragraph, no one should blame you for that. As soon as you start quoting whole sentences, you should make that clear though. If you feel like you are just repeating the whole paper in (as good as possible) your own words, take a step back and think about what you want to achieve with the literature review. You want to give your reader an understanding of what has been done and is currently been done in your field. This should enable the reader to both understand your work, and also understand that your work is a viable contribution to current research topics. One way to do this and avoiding copying papers is to chain multiple together. Think about what you want to discuss, then discuss topic X and put all sources for this topic into your text where appropriate.
Make sure that your citations (bibtex or whatever you use) are all in the same style. Especially if you pull them of the Internet, they might differ, e.g. some places put "Lastname, Firstname", others put "F. Lastname" or "Lastname, F.". You can avoid this, to some extend, by always using the same source for your bibtex code (e.g. google scholar), but even there you should check it properly.
Also, if you have multiple citations in a single \cite, try to order them ascending. Simply because something like ", ... this was already shown in [5,18,2]" doesn't look as nice as "... already shown in [2,5,18]".
Of course, the standard advices like "don't cite what you haven't read or don't fully understand" applies, but I guess you are aware of that.


Overall: Don't worry about formal rules too much. You are telling a story, make it good, informative and interesting to read. Do so why following the rules and stay professional as required in your field of course, but don't make the rules your number one priority.

And just for completeness: Also discuss these questions with your advisor, they might see things differently than this random guy on the Internet, and in the end they are the one grading your thesis.