Q: Is an order that violates the constitution (ordering people to stay in their homes), unlawful? What would SCOTUS say?

A: Objection! The question assumes a fact not in evidence! No court has ruled that a stay-at-home order violates the Maryland Declaration of Rights or the United States Constitution. However, should someone mount a legal challenge, and convince a court that it does, then of course it is true that an "unconstitutional" order is unlawful. All unconstitutional orders are unlawful. But that has not been established. It is not established by your or others' opinion of what should or should not be constitutional. If you decide to violate an order before it is declared unconstitutional by a court or competent jurisdiction, then you can expect to be prosecuted or arrested for your actions, and you can defend the charges all the way to the Supreme Court on that defense if you want. Or you can mount a citizen's or taxpayer's lawsuit to challenge the order in court now, and try to obtain a declaratory judgment by the court in your favor. However, if you want a legal analysis of the constitutionality of such an order under either Maryland or federal law, then this is not the forum to obtain such an analysis. That's a subject requiring considerable scholarly and legal research. There are plenty of pundits on TV and elsewhere throwing out their two cents on the subject, but I would not rely on those opinions or base any conduct on their beliefs of what the law says on this subject.