They did meet several times, although I'm uncertain (and dubious) of the supposed meeting between Twiggs, Lee, and Houston. Lee and Houston were definitely on friendly terms, both being Southern Unionists, and Lee even carried a letter from Houston to his cousin Governor John Letcher of Virginia when Lee left Texas.

I'm dubious of the meeting for several reasons not the least of which is the lack of documentation on it (at least I've been able to find nothing to substantiate the meeting). Further Twiggs handed over all Federal equipment (excepting personal arms, flags, and artillery), fortifications, and troops to Confederate Commissioners who secured it. Sam Houston actually attempted to stop this by using the Texas Rangers, but failed. Also I'd point out that while Shaara is a very good author it's a fictional book that's first priority is to entertain and that little meeting between Twiggs, Houston, and Lee is dramatic and adds a little flavor and tension to the early stages of his book.

Shaara does suffer from a rather obvious Southern bias, whether it's Lost Cause bent is debatable. While it certainly incorporates elements of Lost Cause rhetoric he does ignore other parts like the Longstreet bashing so many Lost Cause believers spout and in fact is rather generous towards Longstreet. How much salt should you take? All in all it's a solidly factual book that takes dramatic license with much of the dialogue and interpersonal relationships and dynamics for obvious reasons since we have almost no transcript to go by. I'd say enjoy it as a read, but if you're looking for the benchmark of Civil War historical fact I'd advocate books based purely on the historical non fiction. Shelby Foote's series is a wonderful place (albeit long) to start.