Family returns home from visiting dying relative to find stranger has moved into their house, change

The “sovereign movement”, by whichever of the dozen names you call it, is nothing but twaddle that a few con men use to pray on gullible folks desperation. Almost all the original “sovereign movement” ringleaders are either in prison, have been to prison, are dead, or have been committed. The reason why some people get away with it for years is that they are simply flying under the radar, and have either not been caught, or have not done anything that the government considers worth the expense to prosecute them yet. The whole theory has more holes in it then a sieve, for example:

1) US courts DO NOT operate under “admiralty law”.
2) The fringe on a flag is a decorative feature on inside vs outdoor flags.
3) The government is not allowed to prosecute you because you are an employee of the United States Inc, they have been persecuting people long before that. Becoming a “non-employee” (aka sovereign) does not mean you are outside the reach of US Law, or courts. The same way you are not outside the reach of a foreign government's laws when you travel. You certainly don't have a “strawman” in a foreign country, but watch how fast they will lock you in prison for breaking their laws. The idea that a government has power over you because of a “strawman” is pure BS...
4) The UCC, which much of the movement is based on, has only existed since 1950, and we have been arresting, imprisoning, writing/enforcing laws, since WAY before that.
5) Every state has its OWN UCC, and it's different for each state.
6) No amendment gives you the right to operate a motor vehicle, only travel in one.
7) The establishment of laws by the Fed, state, and local government is constitutionally guaranteed.

There are about a thousand more, but those are a few that come to mind quickly.
If you want to check out some of the case law against this scam, check the aptly named link here:
Idiot Legal Arguments: A Casebook for Dealing with Extremist Legal Arguments

Here's one of your sovereign movement ringleaders, who was on the way home from a lecture engagement about this very topic:

All the papers which he hands to the officer, and later throws in the window before fleeing, is his “documentation” on how he as a “sovereign” is not required to have a valid license, registration, or tags on his car.
Obviously you can see where this landed him and his son...