How to kick someone out of your netflix account?

So my dad pays for our netflix and we only have it set for two people to watch at a time and my sister thought it would be a good idea to give it to our cousin who than gave the password to her siblings. My sister constantly uses netflix and refuses to let others watch it and sometimes my cousins use it. So me and my family can't use it at times. My dad is angry because he pays for it and he can't even enjoy it. So is there a way I can kick them out.