Filter POST field items using other POST field

Hi! I have a problem with a MetaBoxes that using multiple POST type fields.

I have 4 post types for the different structures existed in Mexican Law (Leyes, Títulos, Capítulos and Artículos). I have created a meta box for each one.

In "Capítulos", for example, I have two Post fields (one for Leyes [to select the law on witch it depends] and other one for "Título" [to select the fraction of the law where this "Capítulo" is located]).

The problem is generated because I need to filter to display only the "Títulos" that is registered under the law I selected on the prior field. The logical order for my user is:

1. Select the law
2. Select the title
3. Select the chapter

Note: I'm not using categories because this site require to create a lot of posts of each type and is really difficult for the end user to manage so many nested categories.

Regards!