I don't know what the laws are like in Portugal (maybe you just need to bribe the right person?
) but I had an experience a few years ago which makes me think it would be a can of worms to find that barn here.
My grandmother died at age 97 several years ago and her estate was straightforward because I was the only heir. She lived by herself right up to the end and had a 1962 Rambler which she used to run errands around her small town in Southern Illinois. That car only had something like 12,000 miles on it and I remember her buying it when I was a kid!
There was a really nice neighbor who helped me clean out the house, and he said his kid was really interested in buying that car to fix it up. So I just gave it to him, but then a paperwork nightmare began. Unlike everything else in the estate, transfering ownership of a car from a dead person was really complicated. I ended up having a lawyer handle it for me and she couldn't believe what was involved, including being sent the wrong forms, submitting, waiting, then filling out the right ones. When all was said and done it took all of 6 months to get that done and cost around $500 in legal fees. I don't remember specifics, but the basic problem was that I couldn't sell or give the car away because it wasn't registered in my name, and changing registration when someone is dead is complicated.
If you wanted to sell or register a barn full of cars with no documentation I'll bet it would be a nightmare. I also wouldn't be surprised if some sales tax were due on the value of your windfall. That was another issue in my case, even though I *gave* the car to this kid, the state wanted sales tax based on its estimated value. When he complained about this I reminded him it had already cost me $500 to give it to him!