Not sure I understand all of this without a few pictures but here is a
try.

1. Attaching aprons to top: The attachment should allow for some slip.
They have items called table irons, little metal figure eight type
things with one screw in top, one in apron. Or you can build (l shaped)
wood blocks that screw to the top and fit in a slot in the apron. You
don't need much slip so eeven screws in a sloppy hole will work.

2. Regarding gluning the top: If I understand this right you have a
round top made out of a glued up panel and one of the edge joints in
the center of the panel is failing. Just put one clamp directly
perpendicular to the crack, then another about 10 degrees to each side
of that and again to each side of that. That gives you 40 degrees total
and should easily pull the crack in. I'm talking about a radial
pattern, like spokes on a wheel or slices of a pie.