All perfect praise be to Allaah, the Lord of the Worlds. I testify that there is none worthy of worship except Allaah, and that Muhammad, sallallaahu ‘alayhi wa sallam, is His Slave and Messenger.
It is recommended to make ‘Umrah many times and the reward will be received for all the times. Consequently, if you stay in Makkah for six days and make ‘Umrah every day, then you will get the reward of six ‘Umrahs, not just the reward of one ‘Umrah.
As for making ‘Umrah for a living person, if you intend by it that you gift the reward to him, then you can do it and the reward will reach him, Allaah Willing. But if you intend by it that you perform ‘Umrah on his behalf, this will not avail him unless he is chronically incapable of performing it himself. In this case, he must give you permission to perform it on his behalf and you can do it after making ‘Umrah for yourself.
Finally, making ‘Umrah on behalf of a deceased person frees him of the obligation and the reward reaches him, Allaah willing.
Allaah Knows best.