Can we determine distance between esp8266 and another esp8266

Greetings, I'm doing a project and wanted to know if it is possible to determine the distance between esp8266 modules to determine the position of a robot within a given area.

It depends on how accurate you want to be. You can simply monitor the signal strength, this will give you enough information to determine if it is getting to far away. It is not an exact measurement, just a relative one.
Good Luck & Have Fun!
Gil