I always write elefants in english as well :-(
I wrote "these are elephants" and it was wrong
where do you take the 'these' from? You are giving much more context that provided. The only mandatory particle in English to make it grammatically correct [and coherent with the translation] is the pronoun 'they'.
Why isn't it 'Their elephants' or your elephants?
Son is used with Ellas/Ellos as well?
their elephants would be Los elefantes de ellos/ellas.
their and your are possessive determiners, which are not used in the original sentence.
[ellos/as] son means [they] are. The subject is optional in Spanish and mandatory in English.