Episode 5 of the Habitable Planets Series takes a look at double planets and what sort of conditions would prevail, or need to prevail, for them to be Earth-like. As well as the Rocheworld, a special case of Double Planets where the two planets either share an atmosphere or have even begun to merge together.

Orbital Period Calculator:
http://www.calctool.org/CALC/phys/astronomy/planet_orbit
Note: make sure to set units of both bodies to Earth Mass and period to hours or days if trying to look at double planet cases.

HP05 - Double Planets And Rocheworlds

Isaac Arthur