I'm not sure about that. I'd like to think that my cats will be in Heaven, but at the end of the day, it's God's decision.
Do animals have souls? I don't know, I don't remember reading any scripture on the matter. Some people say they don't, but they may just be getting confused with the fact that they don't have free will.
(side note)
If animals don't have free will, then presumably they can't sin and they worship God instinctively. But on the other hand, I see animals comitting homosexual acts. It's all very confusing.