At the bottom of our new land are several hollies that have self seeded. Three of them very close together are about 25' now and a lovely shape so we hope to preserve them. However several smaller hollies are growing up in front of them, I would guess about 10-20 of them. Some of them seemed to have layered ( is that the correct term? ) from hanging branches, others possibly seeds? or suckers? None were very big and we have cut them all back as we do not want a holly forest.
We would like to prevent regrowth. Digging out the roots will be impossible because of the holly branches above. Would it be safe to spray them with some sort of root killer or would that compromise the main trees if they are growing as suckers?

Also, once the hard landscaping is finished we would like to plant a few shrubs in front the hollies. The hollies would be on the eastern side of the bed so shade would not be a problem. If we kept them well watered till established should there be any problem with planting near these big trees?

Holly can send up suckers, so a herbicide would not be the best idea.

I would dig out as much of the tree's you wish to remove, put down a heavy duty membrane and new topsoil on top of that.
Plant into the new topsoil.
There should be no problem planting there so long as suitable plants are used, yes water well for the first season (if needed), once they are established they shouldnt be a problem.