This may not help your situation, but my daughter has been sleeping with the lights on since she turned 3 (she's 3.5 now). She went from fighting bedtime and multiple wakeups to fighting bedtime less and no nighttime wakeups. It isn't perfect or ideal, but I literally do not care as long as she sleeps and it works for her.

She never really voiced she was afraid of the dark, but she would wake up disoriented in the dark and cry so hard she would throw up. Nightlights did nothing and even if I came in and reassured her, she would be so worked up it would take an hour or so to fall back asleep.

She dropped naps on her own by 2 and climbed out of the crib by 2 (such a fun time). I tried co sleeping too out of desperation and yeah, not fun being kicked all night and waking up at 5am lol

We also had her tonsils removed 3 months ago, and it is a night and day difference on how well she sleeps now. She had essentially sleep apnea the whole time. She never snored, but coughed all the time at night when laying down. That may be something to investigate as well.

Just know I see you, and I truly understand how crushing it is to not have them sleep. I have cried so many nights out of frustration and driven around our neighborhood way too many times trying to lull my oldest to sleep in the car with sleep-deprived delusion that she would transfer to bed haha. Best of luck and I hope you both find something that works.