NathanaelB, A pity you missed reaching the summit ... nice view at the top !
We did it in Oct 2015, via a car shuffle: Park one car at Round Flat Firetrail. Park the other car at Mt Allen Firetrail. Then walk from one car to the other, climbing Tinderry Twin & Tinderry Peak in between.
Photos and my report of the trip is in this link:
http://mntviews.blogspot.com.au/2015/10/tinderry-twin-tinderry-peak-nsw.htmlAt the Tinderry Twin summit, there is face-like rock ... most interesting ... see photos #17, #18 of the above link.
The Jack Russell Terrier dog you mentioned ... She also accompanied us all the way ... climbed both Tinderry Twin & Tinderry Peak with us ... really amazing, considering that she is only a small dog !
The 2 rocky outcrops in my report are also very interesting (Photos #32 - #48). It is worth a separate trip just to explore them.