Astronomy-wise, the 'mutual Lagrange' placement isn't necessary, or even really possible without an implausibly exact match in the masses of the two bodies. Instead, you have two options:
First, you can just accept the tidal stresses. If both planets are relatively metal-poor, the natural radioisotope heat at their cores will be lessened and overall vulcanism only somewhat higher than Earth's. Or you can give them comparable densities, and volcanic zones bigger than the safe ones; eruption and quake frequency will still probably not be that much higher than Earth's tectonic zones - Japan, Italy, and California come to mind - just more widespread.
Second, you can let the worlds lock to each other - as the Moon is to Earth - and get their 'day/night' cycles from the progression of their mutual orbits. This is, as I understand the astronomy, the more likely case anyway. There are worldbuilding guides out there on the internet that actually lay out how to calculate the distances, orbital periods, and relevant Roche limits; the two-planet system I calculated for one of my own stories involved one planet substantially larger than Earth and another a little smaller, and their twenty-eight hour orbit was still well short of the point of tearing each other apart.
The larger world also took up a sixty-degree arc of the smaller's sky.
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"V, did you do something foolish?"
"Yes, and it was glorious."
First, you can just accept the tidal stresses. If both planets are relatively metal-poor, the natural radioisotope heat at their cores will be lessened and overall vulcanism only somewhat higher than Earth's. Or you can give them comparable densities, and volcanic zones bigger than the safe ones; eruption and quake frequency will still probably not be that much higher than Earth's tectonic zones - Japan, Italy, and California come to mind - just more widespread.
Second, you can let the worlds lock to each other - as the Moon is to Earth - and get their 'day/night' cycles from the progression of their mutual orbits. This is, as I understand the astronomy, the more likely case anyway. There are worldbuilding guides out there on the internet that actually lay out how to calculate the distances, orbital periods, and relevant Roche limits; the two-planet system I calculated for one of my own stories involved one planet substantially larger than Earth and another a little smaller, and their twenty-eight hour orbit was still well short of the point of tearing each other apart.
The larger world also took up a sixty-degree arc of the smaller's sky.
===========
===============================================
"V, did you do something foolish?"
"Yes, and it was glorious."