Is it possible to measure distance with signal strength?
Is it possible to measure the distance between two devices by using RF signal strength if the devices have no obstructions between them? If so then can 2 or 3 be used to get distance and direction?

It is theoretically possible to measure distance between two devices using the signal strength of an RF signal. However, that is not a common approach, and it is likely to be impractical.
You mention &quot;obstacles&quot; and that is one problematic area.
Another problem area is that no antenna is perfectly omni-directional. Changes in antenna orientation will affect signal reception, which in turn may be wrongly interpreted as changes in distance. This may be overcome by adding more transmitters.
Yet another problem area is calibration. It is not insurmountable, may not be terribly easy either.
A more practical way to triangulate position, I think, is to have the transmitters sending synchronized pulses or modulations, and comparing the time/phase differences received. This approach is immune to changes in the amplitude due to antenna orientations and attenuation due to obstacles. This is also the principle upon which GPS works.