This isn't something very special, just something that needs clarification in my opinion.

I'm fairly certain everyone here knows of the 5 main TES games (Arena, Daggerfall, Morrowind, Oblivion, Skyrim) and their expansions. I'm also fairly certain everyone agrees that these are canon, right? Right.

Well, there have been a couple of things that have been bothering me -- indirectly. With this I'm talking about the ''spin-offs''.

In my opinion, they are canon, ESO, TESL, Travels, TESA, all of them, canon. However, due to the rather large amount of conflict regarding the canon-topic I'm wondering, can someone clear this up?

All are canon. New overrides old, but also bear in mind that there's a lot of artistic differences that aren't necessarily retcons. Some of it's artistic liberty, some of it's just that there's more than one version of things in the lore and you're seeing different ones each time (TES 1, 2 and 3 all had different Khajiit breeds, for instance, and 4+5 have yet another one). Apart from that, i'm not sure what conflicts you're referring to, there's been a few here and there but nothing major to my knowledge.