осеннее as-sen-n'i-ji
осенние as-sen-n'i-ji

осеннии as-sen-ni-i

осенняя as-sen-n'uh-juh
я
This is how i imagine saying it. -ие -ее the same, whereas the -ии wouldn't have the Y-sound for the last vowel. And the -яя would be the schwa sound of fathEr, with the last vowel a Y-sound to it.