I have always wondered about that, too. It is looking like they are not likely to be brother and sister, nor married, which is all I have been able to discover. They could still be related in some other way, for all I know.
Here is what I am judging by:
There is an article with a quotation from Arleen that Aaron is not her "husband,&qub68ot; that her husband Chris Lloyd is not the well-known actor, and that she is always having to tell people about what she's
not
(
http://www.soapoperadigest.com/features/days-of-our-lives/features/cat ching_up_with_arleen_sorkin/
).
Arleen's imdb page is cross-referenced with her father, Irving's; and on Irving's page it states he had two children (he died in 2007) and that he was a dentist in the DC area for forty years (
http://uk.imdb.com/board/20815071/bio
and
http://uk.imdb.com/board/22835953/bio
, respectively). [ EDIT: Arleen has
such
a strong New York accent, though, that I really cannot imagine her having grown up in DC ]
Aaron's wikipedia entry states that he was raised in Scarsdale, NY and his mother was a schoolteacher and his father was a lawyer and that he had an older sister and brother (
http://en.wikipedia.org/wiki/Aaron_Sorkin
).