Question

can we find angle between two things using two sensors without any reference between the two sensors

Answer 1

It depends on your choice of sensor.

If you're using two sensors, their information will often be more meaningful if they have a common frame of reference but the act of establishing a frame of reference defines a reference between the two sensors.

You could cheat the problem though. Put a broadband EM source and a prism on one of the items (an easy option would be a visible light and a BK7 or fused silica glass prism). Use a photosensor to measure the intensity across the spectrum and relate that to angle based on how your choice of prism behaves. Take your second sensor and punt it across the room without ever turning it on, thus avoiding any reference to it.