While small, the bodies aren't exactly featherweight, they're both on the order of 10^15 kg, so you'd still need quite the push to move them.
edit: I see now that the system is much flatter than anticipated, which would affect the mass the calculations in the link I posted. Still, they won't be something you just push around.
Even better Jake-Low made a rough estimate of the forces between the two lobes:
And just for fun, I also worked out a best guess for the force between the two "lobes": 1.5 x 10^13 N (assuming Ultima Thule is the same density as our Moon)
Even ignoring that the two lobes are probably vacuum-welded together, it’s quite a large explosion you’d need to permanently separate the two lobes. Granted combinging two rough estimates to get a sense of the escape velocity of one lobe from the other is super messy, but it’s probably informative as a yardstick.
Simply breaking them apart wouldn’t free them, they’d mostly fall back together, you’d need to impart quite a bit of acceleration to one or both lobes to keep them apart. I’m not sure to what extent that would be feasible, but if it was it would take an array of carefully orchestrated nuclear detonations, or huuuuuge rockets along with the nukes.
How much damage would that bomb do?
(I take it not much otherwise you would have written 'what's left of them' instead of 'them')