The buttons are indeed between control and neutral. I think i'll go with the extra button approach. There is no earth wire in the entire staircase system as it only consists of the simplest incanescent fixtures and buttons

The staircase relay btw was replaced (by the same electrician) with new one (circuit breaker-sized), while he left the old one (with light damage to the terminal block but otherwise i think it even works) discarded in the box with the panel. I dont see a need to put a toggle relay instead

Grouping/editing pics right now, will upload very soon

When you install the new buttons, get a roll of glow in the dark tape and put strips of it by each button and on things that could pose a trip hazard.  Running some wires from the shelter battery system to some small LED lights or rough service automotive incandescent lamps in the stairwell would also be a good idea.  These could be connected to a relay running on mains electricity, so that if the mains quits the lights turn on automatically.

I think phosphorescent paint alone would suffice - as the lighting in the staircase is used during the day, it will keep the phosphorescent tape emit _something_

Bad thing is there is no phosphorescent tape available here (not that i know of) - The next usefull thing is to shred some glow in the dark plastic stars and use that

Or just stick a star next to each switch.  Here glow tape is available, but finding places that sell it is hard.  It is also somewhat expensive at ~$10 for a 5yd roll.

The phosphorescent things need nearly permanent intensive illumination from a light source rich in higher energy levels, what mean 24/7 fluorescent or HID lights.

The switch itself contains neon discharge lamp so it does not need external phosphorescence

For marking edges of stairs etc. occasional charge with incandescent lamp (normal use of staircase lighting) is not enough ?

The main problem is, then it glows no longer then half a hour about the lighting is switched OFF. And even for the half hour the light would be very weak, as the "charging" time would be very short and with only weak illumination power (here only shorter wavelength green and blue count, what both are very weak with incandescents)

The lighting there is switched on many times in a day, for a minute at a time. I dont think there is suitable light source other than incandescent. And with the ban getting in, the max available incandescent would be 40W which have somewhat lower temperature (so even less blue and green) than 100W - even if i put 3 of 40W incandescents together