Grant only ever had title to one slave, probably a gift from his father in law. He freed him a couple of years before the War, at a time when he was in dire financial straits, and the price of a slave was somewhere between $25,000 and $100,000 in today’s terms.
Julia Grant may or may not have had title to slaves. Certainly some worked to help her around the house, but it isn’t known if her father transferred title to her, or merely lent them to her. No records.
In any case, they were all freed by MO state action well before the 13th Amendment.
While I understand why ardent Union folks want to fob it off on his wife, the truth is that legal title was held by the husband under law of the time, so they were Grant’s regardless of how they came to him.