Are the yellow lines extending from the front to the back on the underwear, which have a urine-like smell and moisture, ritually impure (najis) and do they render the blanket impure if they touch it?

What we advise is to turn away from whisperings (waswas) and not pay attention to them, for indulging in them leads to great evil. And as long as you are not certain, with a firm conviction you could swear by, that what you find on your clothes is urine, then the original ruling is that there is no impurity. So, build upon this original ruling and do not pay attention to any of these whisperings and delusions.