Since men (typically) only have one X chromosome to start, the X passed in their sperm is identical to that of their somatic cells. So two sisters with the same parents will share one identical X from their father, but the second X from their mother will be different combinations of her two X's.
Edit to add: if genetic recombination didn't happen, then lots of siblings would end up as genetic twins. (50% chance within the same gender). And that would also be identical to the offspring from one crossing one grandparent on each side... Fortunately this doesn't happen!
You can put a woman's X chromosome in a sperm but it'll be labelled "from mum" and not work quite right.
See Prader Willi and Angleman syndrome for examples.