Wrong. You say “had only one slave” - you should have said “owned one slave” - U.S. Grant’s wife owned slaves, which he most certainly “had.”
From the National Park site for Haven (Grant’s farm):
“In 1859, Grant freed William Jones, the only slave he is known to have owned. During the Civil War, some slaves at White Haven simply walked off, as they did on many plantations in both Union and Confederate states. Missouri’s constitutional convention abolished slavery in the state in January 1865, freeing any slaves still living at White Haven.”
Wrong. Ownership of the slave William Jones was clear - the rest were decidedly not. Grant only had one slave.
No, Grant's wife's father owned slaves, one or two of whom were, for a time, sent to work for her. But the actual ownership title was with her father.