Three males between Cassandra and Sybill.

Given the fact that Cassandra and Professor Trelawney share the same surname, I have added in that there must be three male Trelawneys between them. Thoughts? —The preceding unsigned comment was added by HarryPotterRules1 (talkcontribs).

Very likely, though not certain. Her mother, grandmother or great-grandmother might've pulled a McGonagall and kept her surname, passing it on to their child(ren). Alternatively, they may not have married at all; I'd wait until we have a better insight on the Trelawney family before we put that up on the article as fact. --  Seth Cooper  owl post! 22:45, December 9, 2013 (UTC)
The first twenty times I read the books I presumed the "Trelawney" name passed through the maternal line. Your argument, however, is rather convincing. --Hunnie Bunn (talk) 22:55, December 9, 2013 (UTC)