Me and my friend are making a website which has a chat room on it. However since we do not have access to servers, and thus cannot use php or other languages used to make profile systems, the closest we can come is having a prompt appear to ask for a nickname, which can be changed to anything at any time. However this had lead to abuse.

Recently a rather odd group appeared calling themselves a "cult" that apparently surrounds me since im the owner of the site (Don't question it I guess?). They are constantly impersonating me and other important testers/mods on the chat to spread misinformation and lies across the site. On top of that they are saying "not so clean" things under our names too. It is getting extremely annoying and is hurting the reputation of our site. As a result I was forced to bring down 2 major parts of our site, the chat, and one of our popular games that had the same nickname prompt.

How do I deal with this or make it so people can't have the same usernames as somebody else so that I can bring parts of the site up again? 
(It would also help if anybody knew how to make a filter, but thats more of a question for Stack Overflow)