“on the orders of Sheriff Lupe Valdez to get the people inside to sign a court order forbidding them from leaving the apartment.”
Why do we need their consent?
Under Texas law, the controlling health authority, Dallas County Health in this case, is legally required to inform in writing the individuals subject to a public health control order.
Their signatures were likely required for informed consent because the local health authority will be administering medical treatment/tests and because they are subject to prosecution for violating the order. (Kind of like when an officer has you sign a speeding ticket. You make an acknowledgment by your signature.)