The James Webb Space Telescope is scheduled to launch in 2021 and be put in a halo orbit around Sun-Earth L2 soon after. The plan for the Wide Field Infrared Survey Telescope is a launch perhaps around 2025 to another halo orbit also around SE L2.
Both JWST and WFIRST have an approximately known angular resolution at this point in their designs, but is enough known about each planned orbit and their mutual phasing (if any) in order to estimate the minimum distance likely between the two during their possible operational lifetimes and therefore the largest possible angular size of each telescope as seen by the other?
Related but historical rather than future-looking (and lots of good answers!) Have spacecraft photographed each other beyond Earth orbit?
Information on the nature of JWST's planned orbit can be found at:
- What happens to JWST after it runs out of propellant?
- What are the sources of light at L2? How will the James Webb telescope be powered?
- Could JWST stay at L2 "forever"?
- What is the required burn to keep a satellite at a Lagrangian point?
- Can the James Webb Space Telescope basically manage its own orbit if necessary?