The meme artist here is not thinking in enough dimensions. These constraints result in a tetrahedron. So you just need to stand in a triangle formation and have the last guy go in the center and float less than the average human height above ground.
I guess so, also it puts into perspective, how big a feef is. It would have to be 1/4 of the Earth's circumference.
Or maybe they are standing on a smaller sphere.
I think you're fine in just 3 dimensions. If the person to the upper left and lower right have a separate elevation from the other two, this is basically just the shape of a 4 sided die.
Everyone's saying that this works in 3 dimensional space, but this also works in 2 dimensional space such that each side could be at a minimum six feet. The resulting structure would be a rhombus and not a square, with the distance between two of the individuals being much greater than 6 feet, though, which the artist did not accurately represent.