How to change angle between the edge of two joining breps? Help needed

Hey guys/girls,

I would need some help in changing the angle between to breps which their edge is touching at the same two points?

So lets say that we have 3 triangles which are surfaces. The first triangle touches the 2nd one on edge "a". The 2nd triangle touches the side "a" of triangle 1 and the side "c" of triangle number 3. Therefor the 3rd triangle touches with the 2nd one on edge "c". The edges of these triangles (a,c) should allways stay in touch with each other, although the angle of triangle 1 can be different to the one of the 2nd one and the same for the 2nd triangle the angle can change between the triangles 1 and 3. 

Meaning if you you change the height of edge "a" upwards or downwards in z axis then triangle 2 & 3 get pulled by that edge and all lengths of the triangles stay the same no alteration. 

Does anyone have anything on this mater?!