Hi Rudy,
By defining owner groups for the field margin and margin total will solve your issue.
Try this in your xml file:
<record id="view_sale_order_form_inherit" model="ir.ui.view">
<field name="name">sale.order.form.inherit</field>
<field name="model">sale.order</field>
<field name="inherit_id" ref="sale.view_order_form"/>
<field name="arch" type="xml">
<xpath expr="//field[@name='order_line']//tree/field[@name='margin']" position="attributes">
<attribute name="groups">your_owner_group</attribute>
</xpath>
</field>
</record>
If you don't have seperate groups for owner and admin, try by creating a new group for owner
For more info: https://www.youtube.com/watch?v=3JsCu8_Dj3I
Thank you