You can't leave out the "to", it sounds unnatural and it would mean something like "There are big animals." but weirdly phrased. If you put it in the beginning, it sounds as "These are big animals." to me.
Yes, you could say that, but trust me, even it is a good translation it sounds pretty strange. You should prefer "To jsou velká zvířata" or "Jsou to velká zvířata".
I put "They are the big animals", but it was counted wrong. How would you say that?
That would be: "Jsou to ta velká zvířata." (the word "to" in the sentence is a part of the phrase "je to" [for singular]/"jsou to" [for plural])
Ok this makes sense because I had the same issue as the other person. Díky!