Backing up simultaneously two drives are called mirroring. You can not mirror with usb drives. You can do that if you have two internal drives. You can back up one to another using software back up or drag and drop. Hope it answers your question.
I believe so. Reason is most desktops have more then one or two USB ports and backing up your system using either or both depends on you. Question, why would you need two to back-up one lesser drive. Unless, you have a wud of programs to back-up. plus theres a way to save your back-up filrs online if you want.