Yes these concerns is why familial dna comparison is not legal in some states.
Technology has outpaced the legislation and it's going to take a while for the laws to catch up to this uncharted territory.
Yes, that is why I think they used familial DNA to build a family tree to determine who fit the age and location. Then retrieved the discarded DNA for testing before making an arrest. The familial DNA could be disputed but the discarded DNA is the gotcha!