Is there a set way to spread the grout behind/between the tiles so that
they will not crack as they are drilled and the items are screwed tight
up??

In bathrooms, I use a tile cement that is suggested for commercial swimming
pools and then follow the supplied instructions which should ensure that a
full fill is achieved behind the tiles with no air gaps. Take off a tile
occassionally to ensure that the full spread has occured.

To drill the holes, I use a specific tile drill bit (using a bit of fabric
or paper tape to stop the point skipping). Once that is through, I finish
off with a masonry bit into the plaster/brickwork and insert the wall plug,
ensuring any fixings supplied with the fitting itself is discarded.

Christian.