You have to inherit the form view in which button is define for ex: Opportunities and Meetings button is in the CRM -> res_partner_views.xml and Sales button is in the Sale -> res_partner_views.xml(Odoo version 12).

Just add the invisible="1" in button tag in your inherited view.

i found the source that adds the buttons but i think the names of the buttons are dynamically:

<button class="oe_stat_button o_res_partner_tip_opp" type="action" attrs="{'invisible': [('customer', '=', False)]}" name="562" icon="fa-star" context="{'search_default_partner_id': active_id}" modifiers="{'invisible':[['customer','=',false]]}" options="{}">
    <field string="Opportunities" name="opportunity_count" widget="statinfo" modifiers="{'readonly':true}"/>
    <field name="partner_gid" invisible="True" modifiers="{'invisible':true}"/>
    <field name="additional_info" invisible="True" modifiers="{'invisible':true}"/>
</button>
           
<button type="action" class="oe_stat_button" icon="fa-credit-card" name="301" context="{'search_default_partner_id': active_id}" modifiers="{}" options="{}">
    <div class="o_form_field o_stat_info" modifiers="{}">
        <span class="o_stat_value" modifiers="{}">
            <field name="payment_token_count" widget="statinfo" nolabel="1" modifiers="{'readonly':true}"/>
        </span>
        <span class="o_stat_text" modifiers="{}">
            Credit card(s)
        </span>
    </div>
</button>

so how can i hide such buttons?

Inherit the form view and add invisible attribute for the fields which one is not required

If you wan't to disable it in the current browser window,

You can goto developer mode and in the form view of partner, click on the bug icon, --> edit form view.

In the view definition, find where  the button is defined and give an attribute named

invisible="1"

For example, if your button is defined as 

 <button name="graph_function" type="object" class="oe_stat_button" icon="fa-sitemap">Relation</button>

You can then add invisible as 

 <button name="graph_function" type="object" class="oe_stat_button" icon="fa-sitemap" invisible="1">Relation</button>

Inorder that you want to hide them permanently, you'll have to do backend coding by inheriting the view and adding the attribute "invisible" for the button(s).