What will you do after you submit the final manuscript and if the journal editor in the review process for your article asks you to cite articles from his/her journal?
As a personal view, I will consider the editor's suggestion to cite articles from his / her journal if there are articles there worth citing. For me, such suggestion by the editor implies that the manuscript I submitted is not yet 'final'.
Yes. I agree with Romer. If the references suggested by the Editor are worth citing, then they should be cited. Otherwise you should explain the situation and make the Editor understand that his suggestions are not going to improve the quality of the MS in any way.
It depends on why you are being asked to cite the articles. If the articles are relevant and central to the submitted manuscript, then it would wise to not only cite them but discuss them. Sometimes the journal that you submit your manuscript to for peer-review specializes in your field and has published relevant articles of importance which would add to your literature review and/or discussion. It is not just the citation that is germane here but whether the suggested material will improve your article. If you are just asked to cite the articles solely because the journal is trying to increase their impact factor, this would not be a legitimate suggestion or request.