It's been interesting reading this as I have 3 daleks and I keep filling the first 2 up and every time I come back to fill up there is more room so something has to be happening in the bottom of the daleks. The one started last year had reduced to 50% volume over this year and I have now filled the 2nd to the top yet again.
I would use them in rotation ... have one "filling" and when full then fill a different one (emptying it first). As JayG said lifting off the Dalek should be doable - IME it might need shoulder-barging a few times, in different directions, to loosen it enough to then lift off.
You could cycle them round, so when a bin is full use that as the excuse/reminder to lift the top off the oldest, and the middle age one, and mix combine them into one, and then "turn" you youngest into the middle-age one. At some point you will decide that the oldest one is "done" and treat that as a pile to be used, rather than re-incorporating it with the middle-aged one. But that's verging on having a proper regime for making hot compost, so depends how much work you want, how desperately you want really good hot-bin compost (that's not to be sneezed at, just not all that easy to achieve IME).
The easier route is just to go with "Fill and then leave to itself", lift off the Oldest and site at a new position and start filling that (and use the stuff that came out of it).
I saw a YouTube of an award winning allotment holder. He had three bins, and when Bin A was full he emptied Bin C, turned B-to-C and then A-to-B; his bins were deliberately of different sizes, allowing for how much they would shrink during composting, so he didn't have the issue of "shall I combine the two oldest batches". He had been doing it for years, everything was pristine and regimented, as you might expect for an award winner
, so that might be something to aspire too ... but aspiring to it is all that I, personal, intend to do about it!
Is it worth adding some leaf mould into the compost that is going into Bin 3
No, I wouldn't. Waste of good leaf mould, and its bugs (fungus) are not the same as the ones needed kick-start the compost process (bacteria). Would be better to put fresh manure in the compost bin to accelerate it - or Pee on it each day, that will make a big difference.
Leaf Mould is best for planting trees and shrubs with, it has similar fungi (and will stimulate the growth of them) to mycorrhizal fungi and they are expensive to buy. Good as a soil conditioner too, if you can make enough of it.