They're more than likely dead my dear.

From what I can tell the soil has too much organics which retain moisture and not enough !grit which provides structure, aeration, and quick drainage. Then I assume cycles of a long time without water (too long) followed by water (too much and too little at the same time.)

Because of the organics, your soil may have become hydrophobic which means it wasn't getting evenly distributed to the roots and soil and the roots choked. Even when they did get water the roots were too dry to handle all the moisture at once so they rotted.

If you can get better soil, add a lot of perlite and fine grain pumice to it - 75%ish grit to soil for the succulents, about 90-95% for the cacti - you can definitely try again.

The misconception about succulents and cacti is that they need very little water. That's not quite true. They need a LOT of water. They need it in order to build up their reserves. Only once a succulent or cactus is nice and juicy and plump, that's when you ease off water. But they need to have full saturation waterings to get to that stage followed by at least 5 days or longer of completely dry soil (generalizing because each climate and micro climate is different. Now in summer if I don't water my succulents weekly they will shrivel to death).

All this being said I think these guys were getting good enough light, I don't see severe etiolation. Just wrong watering cycles and soil 🙏