Now I will admit my first thought on reading this was “holy crap, they are so dead” - but it turns out, from their linked website, they have previously run the length of New Zealand - 51 marathons in 51 days. So…maybe?
Eddie Izzard managed something similar with no training. 43 marathons in 51 days. He was going to do another bunch in South Africa but called it off due to “unforeseen medical complications.”
The term for people like that is ultrarunners. There are more of them. Many have physical differences from the rest of us, so that doing this is easier for them then it would be for us.