Let me start with this: No matter what your goal is, allowing unmoderated edit access to your page is never a good idea! With guests, do you really mean not-logged-in users?
Assuming you mean "specific people with a login", why not let them use the backend and all of the tools available there to accomplish this task?
You can introduce a new Role and limit that to just being able to edit whatever pages you need them to.
With this approach, you do not have to be concerned about validating and sanitizing your form which in turn is another possible weak spot in itself.
If not, there is the PRO Module "FormBuilder" which might come in handy in your case. It particularly lets you create pages from form submissions (even unmoderated). With it's hookable interface, you can add whatever functionality you need.