Anthony Daniels (the actor who plays C-3PO) describes the filming of this scene in his 2019 autobiography. He identifies these objects as ear trumpets:
"Sir, if you'll not be needing me, I'll close down for a while."
Maxi flicked an external switch he'd rigged earlier. Threepio's eyes went dark. It sounded as though I would have the morning off.
"I seem to have found it."
They were looking into space. Moments before, Props had put a small oil can on the table. Sir Alec and Mark stared at it before it was whisked away. The actors kept gazing at the empty space as they said their lines. Eventually, George would superimpose the classic shot of Carrie's hologram, and Obi-Wan and Luke would be looking right at it. But at the time, there wasn’t much to admire, except the strange objects on Obi-Wan's coffee table – weird, trunked, upside-down cups. I asked. Of course – antique silver ear trumpets. Props are ever so inventive.
— Anthony Daniels, I am C-3PO: The Inside Story (2019), Chapter 19: "Magic" (emphasis added)
An ear trumpet is a non-electronic hearing aid that concentrates sound for a person holding the narrow end to his or her ear. These devices have a variety of shapes, including a form that matches what we see in Star Wars:
— Source: How the Victorian Era Invented Transhumanism
— Source: Swords to Ploughshares, and Aircraft Carriers to Ear Trumpets
You mentioned a continuity glitch:
There is a third object, a dark clay vase or amphora, that appears and disappears between shots (probable goof)
This may be the oil can that Anthony Daniels describes the film crew using for setting the actors' eyelines.