I know that you have probably checked out the possiblity that your Ach was actually ASH. I was looking at a listing for an Eliza Ach in Halifax County, NC when I realized the name was probably Ash because there was an Ash family living near by. That made me think again that I know the Ashe surname is in southside VA. Arthur Ashe was from Richmond. If you have looked at the census in PG county, you have probably also seen the Ash surname listed there.
What do you think? Another thought. Since Paul has found them in DE to you think there was a connection the Quakers? That might explain how they ended up in VA from DE.