Since there have been no responses to the second part of your question, I will offer the following:
Both expansive and expensive are pronounced with the emphasis on the second syllable. The difference is in the pronunciation of those syllables, with expansive having a short “a” sound and expensive having a short “e” sound.
In the case of expansive, the second syllable is “pan,” which has a short “a” sound. Note: Although it is not related to the word expansive, you may recognize “pan” as an English word that means a kind of shallow cooking pot. It rhymes with and should be pronounced like other English words that you may know, such as can, fan, man and ran.
In the case of expensive, the second syllable is “pen,” which has a short “e” sound. Note: Although it is not related to the word expensive, you may recognize “pen” as an English word that means a kind of writing instrument that uses ink. It rhymes with and should be pronounced like other English words that you may know, such as den, hen, men and ten.
I hope this helps.