Delete old articles or perform redirect to the new one covering the same topic?

Take the two older articles, update both of them with references to the new article (e.g. add an editor's note with a link to the new article to each), make sure that the modified dates for the old articles' URLs on the site's XML sitemap reflect the update, and leave the canonical tags as self-referencing. I suggest this other method because 301 redirects work best to pass "SEO juice" (sort of a unreal concept to begin with but whatever) when the previous content at the start URL is near identical to the new content at the target URL. Since you said that only the topic is the same between all three and that the new one is published already, it would be better to simply work with interlinks.