The geometry used for the Boolean operation needs to overlap by at least the endmill radii to ensure that corners are cut cleanly, so:
(using the #112 with a radius of 0.03125")
Duplicate all the geometry and drag the duplicates back into registration.
Select the diamond and the surrounding rectangle for the Boolean operation:
and choose Boolean Intersection:
Select the new shape and shift click on a duplicate of the diamond to make it the key object and choose Boolean Subtraction:
Repeat for the other side with a suitable offset for the #102 endmill: