Sounds like we're all in agreement.
Suggested size and ability scores?
Elephant: Str 30, Dex 10, Con 21, Int 2, Wis 13, Cha 7
Mastodon: Str 32, Dex 11, Con 23, Int 2, Wis 10, Cha 5
Oliphant (from upthread); Str 28, Dex 11, Con 21, Int 4, Wis 15, Cha 11
Int is, of course, going to be 2.