Hi Joy,
We have very limited into on Arabella Turner's siblings and parents. What I got came from Steven David Waddel's family page (rootsweb worldconnect project) and we haven't verified the info yet.
http://worldconnect.rootsweb.com/Thomas Turner
born circa 1729 in Northern Ireland and died Mar 24 1789 in Harford Co, MD. He married Martha [LNU] who was born circa 1732 in Northern Ireland.
Known children:
Andrew [circa 1750]
Sarah [circa 1763]
Catherine [circa 1764]
Samuel [circa 1768]
Arabella [circa 1771]
Margaret [circa 1771]
Sorry we don't have more info. We've been working on other lines. I can tell you more about the Bay family that Arabella married into ...