You've got yourself a bunch of fairly confusing issues. Typically under state law if a person dies without a will, the assets go to spouse/children and if none "up" to parents, etc. If his father survived him, his estate would go to his father and now be a part of his father's estate, but it has to get there so you need an attorney to being the process.
The father's probate would only handle assets he actually owned so if this house was not owned by him it would not go under father's will. Find yourself a local probate attorney to run through the scenario.
This is not legal advice nor intended to create an attorney-client relationship. The information provided here is informational in nature only. This attorney may not be licensed in the jurisdiction which you have a question about so the answer could be only general in nature. Visit Steve Zelinger's website: http://www.stevenzelinger.com/
The complexities of your questions are impossible to fully address in this format. Therefore, you need to meet with a local probate attorney. However, depending on the intestacy laws in WI, then the nephew (if your brother's son) would be the first, after a spouse, to inherit under intestacy law. Therefore, the nephew is entitled to these assets. But, if the nephew is not your brother's son, then it would be improper for him to receive the truck and other assets. A probate must be filed in this case and if you are the closest heir, then you would likely be appointed the personal representative. However, like was said before, because of the complexities of the situation you need to hire a competent probate attorney.
My responses are of a general nature and not having the opportunity to get all of the background may mean that they are not complete. I may not be a licensed attorney in the jurisdiction where you are seeking advice and is based solely on the laws and my expertise in those states in which I am licensed. Therefore, this advice can provide a good foundation in seeking quality legal advice in your particular area.