The "Mastering the Rubber Guard" DVD is where all the Half Guard, Rubber Guard and Spider Web fundamentals for the system are on, whereas the Mount, Back and Twister and Truck are in the Mastering the Twister book.
Fundamentals for top game and bottom game differ respectively which is why there is two books. Yeah, lockdown and its options should be learned first so MTRG book and dvd. When you start sweeping and spend more time on top MTT.
Alder posted several videos of Brent teaching some really basic material that I though was really good, too. Definitely worth committing some time and drills to.
"The lockdown is not the 10th Planet gospel; an open mind is the 10th Planet gospel."
- Amir Allam