partner-contact/partner_firstname/views/res_partner.xml

<?xml version="1.0" encoding="utf-8"?>
<openerp>
<data>

<record id="view_partner_simple_form_firstname" model="ir.ui.view">
    <field name="name">Add firstname and lastname</field>
    <field name="model">res.partner</field>
    <field name="inherit_id" ref="base.view_partner_simple_form"/>
    <field name="arch" type="xml">
        <data>
            <xpath expr="//field[@name='name']" position="attributes">
                <attribute name="attrs">{
                    'readonly': [('is_company', '=', False)],
                    'required': [('is_company', '=', True)]
                }</attribute>
            </xpath>

            <xpath expr="//field[@name='category_id']" position="before">
                <group attrs="{'invisible': [('is_company', '=', True)]}">
                    <field name="lastname"
                           attrs="{'required': [('firstname', '=', False)]}"/>
                    <field name="firstname"
                           attrs="{'required': [('lastname', '=', False)]}"/>
                </group>
            </xpath>
        </data>
    </field>
</record>

<record id="view_partner_form_firstname" model="ir.ui.view">
    <field name="name">Add firstname and surnames</field>
    <field name="model">res.partner</field>
    <field name="inherit_id" ref="base.view_partner_form"/>
    <field name="arch" type="xml">
        <data>
            <xpath expr="//field[@name='name']" position="attributes">
                <attribute name="attrs">{
                    'readonly': [('is_company', '=', False)],
                    'required': [('is_company', '=', True)]
                }</attribute>
            </xpath>

            <xpath expr="//field[@name='category_id']" position="before">
                <group attrs="{'invisible': [('is_company', '=', True)]}">
                    <field name="lastname"
                           attrs="{'required': [('firstname', '=', False)]}"/>
                    <field name="firstname"
                           attrs="{'required': [('lastname', '=', False)]}"/>
                </group>
            </xpath>

            <!-- Modify inner contact form of child_ids -->
            <xpath expr="//field[@name='child_ids']/form
                         //field[@name='category_id']"
                   position="before">
                <group attrs="{'invisible': [('is_company', '=', True)]}">
                    <field name="lastname"
                           attrs="{'required': [('firstname', '=', False)]}"/>
                    <field name="firstname"
                           attrs="{'required': [('lastname', '=', False)]}"/>
                </group>
            </xpath>

            <xpath expr="//field[@name='child_ids']/form
                         //field[@name='category_id']"
                   position="attributes">
                <attribute name="style"/>
            </xpath>

            <xpath expr="//field[@name='child_ids']/form//label[@for='name']"
                   position="before">
                <div class="oe_edit_only">
                    <field name="is_company"
                           on_change="onchange_type(is_company)"/>
                    <label for="is_company"
                           string="Is a Company?"/>
                </div>
            </xpath>

            <xpath expr="//field[@name='child_ids']/form//field[@name='name']"
                   position="attributes">
                <attribute name="attrs">{
                    'readonly': [('is_company', '=', False)],
                    'required': [('is_company', '=', True)]
                }</attribute>
            </xpath>
        </data>
  </field>
</record>

</data>
</openerp>