2. Rosslyn Chapel was built by masons, or certainly masons were involved with the building, possibly Knights Templars / Masons. I don't really have any in-depth information available about it that is not already public, such as in books like "Holy Blood, Holy Grail", which has a lot of truth in it and is the book (non-fiction, scientific research) which Dan Brown stole the story for the "Davinci Code" from. I highly recommend that book for anyone interested in the topic of the templars, masons, jesus, the "holy grail", etc. Very resourceful. You can find it on amazon: Amazon.com: Holy Blood, Holy Grail Illustrated Edition: The Secret History of Jesus, the Shocking Legacy of the Grail (9780385340014): Michael Baigent, Richard Leigh, Henry Lincoln: Books
3. Holy Grail is the bloodline of Jesus, pretty much, and in spanish, latin, italian and french the word for "blood" is sangre, sanguim, sangue and sang - fairly obvious connection to the corresponding translations of "Holy Grail" in same languages, as your examples "san graal" and "san greal". In other words, Jesus didn't die at the cross, and he had children that lived on and presumably his family line is still around and some orders claim to be directly connected through "bloodlines" to Jesus, or knowing who these "children of Jesus" are. Personally, I do not know who that would be, but it seems probable enough from other knowledge I have.
4. William Sinclair was the man who founded Rosslyn Chapel back in the 1400's, most likely he was a Grand Master of Freemasonry and probably also a Knights Templar, and several of the later Sinclair's also became Grand Master's of the Grand Lodge of Scotland.