And if not, what prevents the second 'ejectee' being eviscerated in the rocket plume from the first ?
Not strictly an ac but on the US Gemini spacecraft which used ejector seats instead of an escape rocket the seats were angled at 12 degs from the vertical to ensure that the 2 astronauts diverged during an ejection.
In their case they were departing from a closed pressurised cabin full of 100% oxygen which might have reacted unfavourably with the rocket exhaust! In at least one test the doors also failed to open in sequence & the test manikins went through them on their seats which would've killed any human occupants, this might explain the reluctance of the astronauts to pull the handle on Gemini 6: the engines shutdown after ignition but with a cockpit indication that the rocket had started to lift off. Wally Schirra should've pulled the handle, would've had he been in the sim, but went with his gut instinct that the rocket hadn't moved. The 'right stuff' indeed.