Hilarious! But it's time for your resident weapon-understanding himbo to cut in.
Four's fine. He's holding the sword just fine. You can hold a sword by the blade. It can't cut you without someone pulling or pushing on it, not unles you run your hand along the edge, which he's not doing.
So the way Four has it clutched? Totally valid and mostly safe. It's resting in his arms, tucked against his shoulder. He's supporting the weight mostly under the break and resting his other hand over the edge for balance. He's not gonna lose his fingers unless Warriors or the Blacksmith decide to try and take it from him without warning, and even then, he won't lose a finger. He'll get nicked. At which point, he'll probably bleed a bit, wrap the injury, and move on.
A sword can't take your finger off that easily. Have you ever tried to chop an uncooked carrot? It's about like trying to use regular grip pressure to try and cut through a carrot. It takes excessive pressure to do that. It's not going to just slice off his fingers just because he touched the edge. Swords aren't all that powerful on their own, and Four (and clearly Jojo) knows that.
Some of ya'll have never handled a sword, and it shows. I'm begging you to pick up a pocket knife and hold it by the blade. You'll instantly see what I mean. With blades, force must be applied to cause injury. I say this as someone who widdles, swordfights, and has been injured by a sword. I have a scar from a katana. It's small, yes, but I know what I'm talking about.
There must be force. Four is fine.