Can balloons be stacked in a climable daisy chain to the edge of space?
As you go higher the pressure decreases which means that the density of both the air and the lifting gas goes down.

That means that the higher you want to go the bigger the balloon you need for a given lifting force. Eventually you reach a point where it is not not practical to make the structure light enough to go any higher. The highest altitude reached by a balloon is considerably lower than the lowest altitude at which orbit is practical.

It also means that as you go higher the wind-area of your balloon increases which will put more force on the tether. The loading from the tether, both from it's weight and from winds at various altitudes will further reduce the practical maximum altitude compared to a free floating balloon.

There is also the issue that in low orbit you need a considerable sideways movement relative to the ground. Most of the delta-v in a launch rocket is spent on gaining the sideways velocity, not in gaining the altitude.