Can i drive my grandmother's car without being under her insurance?

so this is kind of confusing, but basically every car in my family is under my great grandmother's name, and all of my family (other then me) are under her insurance policy. So what im wondering is will it be legal (and will i be covered) to drive a car thats under my great grandmother's name even if i dont have any insurance (but the car does), i know its not really "ideal" but it'll only be for a couple of weeks till i get added to her insurance policy. thanks!

p.s. my great grandmother's insurance is allstate, i live in texas, and i dont live at the same residence as my great grandmother.