Okay, let me think through this...
If Sans threw anything at Asta, he could either take it, dodge it, block it, or reflect it, due to his strength, agility, and swords. He could probably avoid things being thrown at him without his Black Asta form.
Asta's swords, without Black Asta, have cut through SPACIAL Magic--a rare type of magic that can manipulate space itself.
Asta's cut through and reflected magic fire, magic threads, magic blasts, and even magic smoke and mist.
Black Asta can still be affected physically; he might be pushed back, but probably wouldn't be burned or anything like that.
The bones are tricky, since we don't know the full extent of their power.
I've not seen anything in the RP about somebody attacking Sans' bones; if so, please inform me.
However, Asta's cut through Sekke's Bronze Magic, as shown in the video above. He's also used his sword to withstand the entire magic pool of a noble; the social class known to have high magic abilities. I'll leave whether or not he can cut Sans' magic bones up to debate.
He's reflected a Magic Bullet, cut through a knight made entirely of sand, and even sliced Magic Chains as well as Light Magic, which is notoriously powerful in Asta's world.
His Anti-Magic also makes him resistant to tracking methods that are magical in any way. Sans probably wouldn't be able to sense his soul because where there should be magic in him, there's natural Anti-Magic that's hiding his presence from anything magical.
Keep in mind that in Asta's world, magic can be naturally sensed by other magic users, like ki in Dragon Ball. Asta's abilities make him completely under the radar in his own universe. He's used this to his advantage twice; once when fighting a Smoke Mage, where he was used like an untraceable cannonball to deal the final blow.
The second time was when they were fighting the main antagonist cult's leader.
You might need some insight for this; I went over the Magic Knights already. Asta, some of his squad-mates, and his squad leader were up against this guy.
The battle got so serious, three other Magic Knight captains had to step in.
Keep in mind, these guys are no pushovers; not by a long shot.
The Magic Knights are powerful warriors; their leaders are no different. The Black Bulls are already considered one of the worst Magic Knight squads due to their cast; commoners, and only a few nobles in the mix.
Their leader, Yami Sukehiro, possesses a spell so powerful, it can CUT BETWEEN DIMENSIONS. And some of the other captains are stronger than him.
This tells you how powerful all of the big bosses are in Black Clover.
Anyways, while the leader of the opposing cult was distracter, Asta and Yami devised a plan.
Using Spacial Magic, Yami warped above the leader in an attempt to get a clean hit on him.
Everybody immediately sensed him; no surprise.
But now their attention was on the two of them; their focus was on Yami, and Licht, the opposing leader.
Despite their power, and their focus, not one, NOT ONE OF THEM, noticed Asta.
Within the chaos, Asta leapt up to get a massive strike on Licht using the Demon-Slayer Sword.
Right before the final blow by Asta, Licht noted that the ONLY PURE reason that none of them could see Asta coming, was because of his powers; more accurately, his lack of magic.
As such, to restate, he's immune to all forms of magic tracking. So I doubt Sans would even be able to see Asta coming.
Besides, if they were to trade blows, Sans' magic would be passively drained by Asta's swords, or Black Asta's aura. And his ki sensing plays into a big affect as well.
Moving onto J.
J... has no magic, I presume. This makes things harder.
But J is a living being, and therefore he has ki.
Asta would be able to sense this ki, and as such, would be able to see him coming.
And, I stated earlier that Asta has enhanced instinct.
Not only that, but he can keep track of things that are moving much faster than he can.
And... shoot, there's a clip somewhere...
Okay Comic, I have a new speed for you. And this isn't even Black Asta.
So, I mentioned Licht, leader of the Midnight Sun cult.
But the leader isn't always the strongest.
Asta had to once face someone more powerful than Licht, WITHOUT Yami.
Allow me to present Asta vs Vetto the Despair.
