home-brew basement stairs helper
If I understand your situation correctly, then you may be in a similar situation as I was at my last house. The landing where the dog-leg begins is big enough for people to get around the corner but not a pin strapped to an appliance dolly.
Here's what I did to solve that problem. I used wood and built a platform that raised the landing up by one stair-height. For me, the addition of one more stair's worth of width was sufficient to allow me to get the pin down the stairs to the place where it had to turn 90 degrees while still strapped to the dolly.
There was NOT enough extra space for me to be able to spin the dolly plus the pin 90 degrees, and then keep going down the final few steps. But with the mod I devised there was enough space to un-strap the machine from the dolly, get the dolly out of the way, and then spin the pin 90 degrees. I then scooted the pin forward towards the edge of the landing, towards the next step down. It was rather precarious so I had my son help spot for me. Once I did that there was enough room to get the appliance dolly back into position and re-strap the pin to it. From there, we could tilt it back onto the dolly and make it down the last few steps and into the basement.
When we moved, I bought an Escalera and with that I also added the extended lower steps you see that are partially painted in black. I wish I'd done that sooner because extending those two lower steps made it all work easily (same process, just going up the stars instead of down.)