I would like to know how can I download/print a single pdf that has multiple reports of the same template.

At the moment I can download only a single report per child, but I want to have them all in a single pdf when I print them from the parent. In my views I use buttons in the header to get the report.

<header>
	<button name="%(action_report_salary_all_details)d" string="Salary (details)" type="action" style="margin-right: 5px;"/>
	<button name="%(action_report_salary_few_details)d" string="Salary" type="action"/>
</header>

My report code for the child model (parent is 'hr.history.salary' and it is in One2Many relation with child):

class ReportSalaryFewDetails(models.AbstractModel):
    _name = 'report.hr.report_salary_few_details'

    @api.model
    def render_html(self, docids, data=None):
        payslips = self.env['hr.history.salary.salary_slips'].browse(docids)
        docargs = {
            'doc_ids': docids,
            'doc_model': 'hr.history.salary.salary_slips',
            'docs': payslips,
            'data': data,
        }
        return self.env['report'].render('my_addon.report_salary_few_details', docargs)

Do I have to create a whole new report so I can call it from the parent or can I modify this code and how to print them all in one pdf?