It will depend if their name is on the deed or just on the mortgage. if it is on the deed it makes them part owner. You should review the deed and if they are, you may want to speak to an attromey on what you can do to protect yourself and your home.
Assuming your parents are only co-signers on the mortgage and they are not on the title of your home as owners, you should be safe. However, I'm just an agent on the internet, it would be wise to seek advice of an attorney of you have a concern.