No, you cannot get life insurance on your parents without them knowing. Life insurance policies are a legal contract between two parties (the policyholder and the insurer) that requires disclosure of all relevant information to secure coverage and determine the premium payment.
In most cases, the person who is going to be insured and their signature are required to get life insurance. You will also need their permission to access information about their health and financial situation, which can affect the premiums and coverage. Because of this, it is not possible to get an insurance policy for your parents without their knowledge and permission.
You can, however, set up a life insurance policy for their benefit. This type of policy still requires their permission and information, but it will be established in your name, and you will make the premium payments. You can keep it a secret if you and your parents decide to do so, but it is important to make sure that your parents know and understand the policy details.
For more information on life insurance and setting up a policy for someone else, you can consult this guide: https://www.thebalance.com/life-insurance-for-someone-else-357356