Is it permissible to go for Umrah with my maternal aunt's husband and his daughters without a mahram?

If the umrah is voluntary, then it is not permissible to travel for it without a mahram, and the husband of the maternal aunt is not a mahram. However, if the umrah is obligatory (the umrah of Islam), then it is permissible to travel without a mahram, provided there is a trustworthy company.