I've yet to see any scripture that supports animals have souls. Animals are referred to in heaven but it still requires a bit of imagination to think of that as any sort of evidence that animals have souls.
Mines an unpopular opinion (and that's all i, or anyone else here, have, opinions) because i think most people Want animals to have souls. And since there is no clear evidence people will interpret it as they wish it to be.
The Bible does not explicity say "Animals/Pets go to Heaven." However, there is alot of support that animals have souls and spirits. There is a lot of support presented on this site:
https://www.rainbowsbridge.com/
(Job 12:9-10 KJV)
"Who knoweth not in all these that the hand of the Lord hath wrought this? In whose hand is the soul of every living thing, and the breath of all mankind."
Job 12:10
In his hand is the life of every living thing and the breath of all mankind.
Revelation 5:8-13
"All creatures recognize Jesus as the Savior of the world and praise God right along with redeemed men.
Psalm 145:-9-10,13,15-21 AMP
Though all creatures are subject to man's cruelty, God loves all His creation and has made plans for all His children and the lesser creatures to enjoy His eternal Kingdom.