How will the company or merc operate when their homes, logistic, families are all living under the GTVA?
1. The GTVA is a political entity founded to uphold a political treaty, the BETAC. As the entity assigned to the protection of the sets of laws that exist under this social contract, it is not allowed to violate them. Simply put,
those how have to enforce the law, have to obey the law. The existence of law breakers does not suspend the rule of law.2. The doctrine of the prohibition of collective punishment applies under BETAC. Long fancy words, made short: Under BETAC you cannot punish a person for the actions of another. Especially you cannot punish someone solely based on association, including family connection, legitimate business ties, and similar.
3. Internal enemies of the GTVA might shelter their logistics into "uncooperative populations", i.e. they might seek specifically to build their logistics base on planets which already have a strained relation with the GTVA. As a result any military or law enforcement action may be delayed by having to navigate the relationship between GTVA authorities and the locals.
4. Internal enemies of the GTVA might exploit the provisions set up for the oversight of civic institutions, e.g. the GTVA version of a "Freedom of Information Act", to gather intelligence and identify and exploit blind spots of the GTVA.
1, 2 and 3 are reasons that in the real world help organized crime to be successful against prosecution.