Assuming my knowledge of Elder Scrolls lore is correct, the dragons are from Akavir. Are these the same dragons as we see in Skyrim? And, if so, why haven't the Dragons tried to take over all of Akavir before branching out to conquer Skyrim and Tamriel?

The Nords collectively seem to have had a relationship with Dragons since time immemorial, seeing as how ingrained it is in their history. It isn't too much of a stretch to say that they also inhabited Atmora. They're semi-divine being themselves, I don't really think they consider any particular region to be their homeland to begin with.

The dragons didn't leave for Atmora until they were pushed out of skyrim by the nords and then out of Morrowind by the cliff racers iirc.

Didn't the dragons come to Skyrim from Atmora with the Nords?

I like to think so.

I find it annoying how little we know of Dragons and their connection to Dragon-land.

If I recall right there was also someone who thought Atmora was actually Kamal. Based on dragons supposedly being from Akavir, Kamal being a frozen hell hole and Atmora eventually becoming a frozen hell hole. From what I've seen the earliest mention of dragons in Tamriel is when the Nords arrived in Skyrim. So I suppose It might be possible or at least the Kamal invaded Atmora sometime in the past slowly changing it into the frozen wasteland it is now and driving the rest of the Nord's out.