It is 100 times less common in google searches than the way Duolingo does it. That does not mean your way is wrong but it might sound odd when compared to the most common way. My guess is most of the time duolingo is judging things like this on mere instinct.
It makes sense but it's not said that way. There's only one "last year:, so "two last years" is awkward. Changing the order makes the time duration "two years", and the "two years" in question are the last two years.
I don't know if it makes a difference in Spanish but in English changing the word order changes the meaning.
I think pasado translates to past. As for 'two last years' I think it would be understood.
If you mean "during" when you use the word "last," then, yes, "over the last two years" is correct.
In my opinion, the wording, during the two last years should not be considered incorrect.
You should report this as a correct alternative interpretation, although it would not work in every context.
When there is no context, "during the final two years" does not work because that means that no more years will occur. However, if you are talking of a duration of time that happened and ended in the past, then "during the final two years" does work. For example, "During the final two years of World War Two ... ."
Say it both ways to any American (assimiliated in US culture) and see if there's a difference in understanding. (There's really not.) I got this wrong for spelling out two instead of using the grammatically-incorrect numeral 2... Laughable.
You are right. You would be understood even though there is technically a difference in meaning. I find it interesting that when I use voice to text DL translates two to the numeral 2, but if you type the numeral, it marks you wrong.