One option is for you to take an ancestry test as well - your brother should show up at the top of your match list, which is sufficient to confirm the relationship with him on wikitree (provided you document it appropriately). However, in order to take advantage of any Y-Chromosome confirmation, he would have to do a Y-DNA test first; those are fairly expensive, and Ancestry doesn't offer them. However, they aren't nearly as useful for more recent history, so I wouldn't be too bothered by that. As far as Triangulation: yes, it's a bit confusing - it's also harder to make work since you need three testers rather than two.