Can I have a signed letter with two other witnesses signing as well for a right to claim possession of personal property form?

When a person dies, all of their possessions [along with items they physically have but are owned by someone else] that are not in a Trust go into their estate. If there is no Will, the items pass according to the law to spouse, children, other relatives, or to the State if there are no heirs. Technically, everything must go through probate, even if there is a Will. Title to property can not be transferred without a probate order. She could not just transfer ownership of the car to herself; there must be a legal transfer [pink slip is evidence of ownership]. You need to speak to her and find out on what basis she claims the right to anything. If she refuses to probate the estate, you can file. It is a costly and messy procedure, but unless you can clearly show title to some of the objects, it is probably the only thing you can do. There is no such form as you request and even if there were it would be worthless.