lots of things can cause an "itchy rash". thousands of diseases and conditions in fact. you and your sister need to be medical examined so that you can be properly diagnosed and treated -- not something that can be accomplished over the internet.
weird rash over body. i got a really itchy sensation all over my body mostly my stomach inner thighs under butt cheeks calfs inner wrists and arms (mostly all). when i scratch i dont feel no bumps sometimes i do get very small bumps when i do scratch a lot. i noticed my sister also has it. what could it be?