multiple dependent dropdown with DB2?

Hello Ray,
I'm having bad times trying to set up a multiple dropdown menu with DB2 and framework plug-ins.

Actually I have a:
- grand-parent select (1) (in main page)
-- parent select (2) (in file inc.plugin1.php)
--- child select (3) (in file inc.plugin2.php)

I use static-plug-ins.

I can succesfully make select(2) changes when select(1) changes.
But how can I make select(3) changes when select(2) changes?

The main page contains the static-plugin that triggers select(2) when select(1) changes).
Where should I put the other static-plug-in (the one that triggers select(3) when select(2) changes)?
Should I put it on the same main page?
Or should I put it on the first plug-in file?
This is totally obscure to me... :(.
Can you explain briefly how this should work?
TIA
tony
Have I to put the static plug-in in the main page?
Or have

I'd have one select on the page itself.

The first plugin with the second select list and a third plugin with the third select list.

Then add the plugin with the third select list to the first plugin.

So the main page has one plugin. The first plugin has the second plugin, and the second plugin has just the final select list.