MS SQL Server was based on Sybase 4.2 as I recall, which is the Sybase release that predated introduction of SMP support. (Internally known as the "boat anchor" though I doubt that name appeared on the contract to sell the code.) Microsoft basically rewrote it, so I would guess there is little original Sybase code left. You can still see the the heritage clearly in features like T-SQL dialect and the Tabular Data Stream wire protocol, both of which were developed at Sybase.
Sybase is not in anyway related to Ingres that I know of other than the fact that Bob Epstein and Mike Stonebraker worked on the Ingres project at Cal. Sybase in fact was considerably different from Ingres in many ways such as use of SQL instead of QUEL, network access to the SQL Server, and specialized features like stored procedures. The Sybase founders did not come directly from Cal or even Ingres but rather from Britton Lee.
Intellectually, somewhat, perhaps. Sybase was a distinct implementation. When it came on the market, Ingres IIRC was still based on QUEL. Sybase had its new T-SQL language and a novel design that made it feasible to use for OLTP. At that time, Ingres and Oracle were usually devoted to decision support, and OLTP was backed by things like VSAM.
You are actually not far off. Sybase was founded by Bob Epstein, who was Stonebraker's student at Berkeley and helped build the original INGRES system.
I've read that SQL Server code was originally based on Sybase code they licensed. Not sure.