FuelPHP model's / fieldset / form

Question

I am new developing fuelPHP and I have 4 questions about it:

1. I am building a form which uses 2 models, I do this:

   $fieldset = Fieldset::forge('register_form');
   $fieldset->add_model('Model_Ntk_User');
   $fieldset->add_model('Model_Ntk_Users_Social_Network');
   

   But some fields has same name, how can I solve that?. I found a method set_form_fields, but not much info about it.

2. In Yii, in example you can build a model using CActiveRecord (if linked to a table) or CFormModel to build Contact forms in example, how this is done with fuelPHP, model_crud?

3. If I use html form (not build using fieldset) how can I use validation without adding the validation rules in the controller, since they are already set on $_properties in the model?

4. I have created an Observer which adds values to fields like ip_added and date_added, but first is triggered the Observers: Typing and Validation, since those fields are set to "not null" Typing observer throw an exception. So far I have fix it making those fields "null" but I think that is bad idea.