Hi,

We can make fields readonly directly through the XML file itself.
To do this, inherit the form view 'crm.crm_lead_view_form' and set the 'readonly' attribute for the desired fields.

Refer to the below code:

    <xpath expr="//group[@name='opportunity_partner']/field[@name='partner_id']" position="attributes">
<attribute name="readonly">stage_id != %(crm.stage_lead1)d</attribute>
    </xpath>

Similarly, you can do it for the other 2 fields.

Hope it helps.