how do i remove apps that cant be removed like mackeeper

MacKeeper's uninstallation instructions actually work, provided you follow them exactly. If you did something that resulted in an incomplete uninstallation, then you may need to install it again for the sole purpose of uninstalling it correctly.

I don't know what Cerberus is, but if you explain what it is or where you obtained it from, perhaps someone else does.

Time Machine provides the quickest way to "undo" something you regret doing, like installing MacKeeper or similarly categorized garbage: Back up your files with Time Machine on Mac - Apple Support

You could try an app like AppCleaner. I have used with good success.