Absolutely not.
The beneficiary has not control over the will. The court will determine who the executor will be.
Assuming the person who made the will is still alive, he/she can do another will or do a codicil to that will that changes the executor to someone else. If the person who made the will is dead, he/she cannot change the executor. Obviously.
how can I become an executor of a dead relative
The power of attorney has no value. The probate court will have to appoint an executor for the estate, who can then transfer the stocks.
The person is still living. The executor can only become authorized by a court order once the person is dead.
That person should sign all documents "(Son), Executor, estate of (Deceased)". If you need a title they can't find, they need to go to DMV and apply for a duplicate.
Yes, a living person can change their will, either by writing a new one or by adding a codicil. In both cases the new/replacement will or codicil need to be formally witnessed to be legal. Once the person is dead or is no longer mentally competent, the will can not be changed. However, depending on the laws of the country in which you live, it may be possible to modify the terms of a will if ALL beneficiaries and the Executor agree to go to court to do this to get a " deed of variation". However, if one party does not agree then the will must be followed as the deceased specified.
Your father's estate owns it, until distributed by the executor. Your aunt does not have title to the motorcycle unless she has a Letter of Authority from the probate court.
If the owner of the guns is dead, you can not get them from the police not being the owner.
So far the dead sea does not have an owner.
No
Generally, in the United States, when a person dies owning real property their estate must be probated in order for title to pass to the heirs legally. Once the title has passed legally the heirs can convey the property by a quitclaim deed to a new owner. You should seek the advice of an attorney who specializes in probate.