as others have said, do get the books.
They are so clear, you can learn from them directly. It's not like buying a technical book that you then need a teacher to "translate".
On the odd occasion I wasn't sure about something I used to email the publishers and a speech therapist would get straight back to me.
It Takes Two is about training you the parent to use the best possible techniques in your interactions with the child. I started with It Takes Two because it's simpler (and to be honest I was too scared at the time to get anything that even mentioned ASD which looking back is daft but hey ho....). This meant that I already had good basic techniques when I started going a bit "deeper".
More than Words is, like the title suggests, about going deeper. It looks at how the child may very well not be "reading the signals" in various different ways when people talk to him/her. I think if you absorb the techniques there it will put you in a position to think very seriously about yet further possibilities that many on here have tried and recommend (PECS, ABA, dietary changes, etc). I had a lightbulb moment about three pages into More then Words and immediately knew that a particular idea had power and would help DS2 (for us it was all the visual learning stuff....)