Is it permissible to combine the intention for 'Umrah for two deceased parents, or is it obligatory to perform 'Umrah for each one separately?

"Umrah is performed for one person only. Therefore, it is not permissible to perform a single Umrah for both your parents simultaneously. Rather, each of them requires a separate Umrah. It is preferable to start with the mother's Umrah due to the merit of honoring her, unless the mother's Umrah is supererogatory and the father's Umrah is obligatory which he did not perform during his lifetime; in that case, the father's Umrah takes precedence. And whoever enters into ihram on behalf of two persons, the ritual falls for himself."