My only suggestion is to ask them to read the creation story in Genesis. After God made the heavens, the earth, the plants and all the animals he "saw that it was good". He then made Adam and gave him dominion over all of the animals.
If the snakes were seen as good in God's eyes, how can they be satanic? If people have dominion over all the animals, how can a snake have the power to corrupt us?
I hope that the pastor wil be helpful in educating your parents. If not, best of luck finding a foster home for your snakes until your situation in life changes.
The Zombie Mama is here!