Fibers do not "have a right" to be in or on items specific to the crime.
Patsy claimed she never wore that red sweater in the basement nor did she paint while wearing it. The paint tote and duct tape never left the basement- they are IMPORTANT parts of the crime scene. Patsy claimed JB put those huge panties on herself. How did JR's shirt fibers get INSIDE the crotch? Patsy was wearing the same clothes from the day before but NOT JR. It was fibers his shirt from the shirt worn the previous night that were found. And for fibers to be entwined inside the knot of the cord, that can only have happened when someone tied that knot.
It isn't the presence of the fibers themselves. Yes, fibers from family members WILL be all over a home. But the presence of the fibers on items that were part of the crime ONLY (duct tape, garrote knot, staged panties, paint tote) are what points to a family coverup.
Your usual fine efforts, DD. But I doubt you'll have much more success than I've had!