Question: “Can you have multiple parent requirements to a single child requirement?”
Question: “Is it good design practice to use a single characteristic of a single subsystem as a part of the solution to multiple requirements of the parent system?”
Answer: The practice has the potential to increase coupling. Whether or not this occurs is technology dependent. The practice has the potential to either reduce or increase cohesion, depending on specifics. The practice has the potential to either reduce or increase connectivity depending on specifics. Coupling, cohesion and connectivity are discussed in the Logical Design module of the Systems Engineering course.
Some examples of the practice applied beneficially: