What is the ruling on picking and selling the fruits of a tree planted by my father 50 years ago in an adjacent piece of land that has been neglected? And what is the ruling on eating from these fruits without selling them? And what should I do with the money I have received?

If the landowner permitted your father to plant a tree on his land as a loan (''ariya''), and he has not yet reclaimed it, then there is no harm for you in benefiting from its fruits, whether by selling them or otherwise. However, if you are unaware of his permission, you can refer to him to ascertain the true situation. If it is established that the father usurped the land and planted in it without the owner's permission, then clarify this so that an answer can be provided.