Is it permissible to go for the first 'Umrah by bus without a Mahram, accompanied by elderly women and daughters of maternal uncles, with the trip organized through an 'Umrah agency and other people present on the bus, and is it permissible for a girl to go if her parents forbid her from traveling with a group of women without a Mahram?

The women mentioned are not your mahrams for travel. A woman's mahram is her husband, or anyone whom she is permanently forbidden to marry. The preponderant view among us is that 'Umrah is obligatory immediately, once, just like Hajj. A woman's travel for 'Umrah without a mahram, but with a trustworthy company, is permissible according to us. However, if her parents prevent her from traveling without a mahram, then she must obey them, unless she believes that 'Umrah is immediately obligatory and that a mahram is not a condition for it. In this case, traveling for 'Umrah becomes obligatory for her, and she is not permitted to obey them in abandoning it.