What is the Miqat to which one must go to renew the intention for Umrah on behalf of deceased parents and enter into a state of Ihram from there, and is it necessary to change the Ihram garments to perform this Umrah?

Repeating Umrah during a single journey, whether for oneself or on behalf of others, is not from the Sunnah. Nevertheless, the majority of scholars have permitted a second Umrah for someone who has already performed Umrah during their journey, especially if they have traveled from a distant place, provided they enter into Ihram from outside the Haram boundary (adnal-hill), such as from Tan'eem. This is what Aisha, may Allah be pleased with her, did by the command of the Prophet, peace and blessings be upon him. The pilgrim can enter into Ihram from any direction outside the Haram, not exclusively Tan'eem. Furthermore, there is no requirement to change the Ihram garments as long as the conditions are met, though it is recommended for them to be clean and white.