You should take balloon from Estrain to West Landing. While the balloon almost close to West Landing, you would see a wood lying on the plateau and please jump out the balloon. this is the entrance to the twin pinnacles. the wood shows that this is the shortest height between balloon and the plateau that characters would not die if they jump, but make sure that your character is in full health. Or you can observe the route of the balloon in West Landing before trying to jump, and you would see the balloon would be very closed to the plateau while it is landing.

Found it - that was tricky! died twice jumping off at the wrong time