Update: I spoke with sibling A at length tonight. We're going to reduce the asking price on the property tomorrow morning to see if we can generate some interest. I'm not hopeful, I looked at the hit numbers on the real estate agent's site since the original listing a few months back and they tailed off pretty quickly. I'm expecting the same again, but we'll see.
We also discussed some options for an outright buyout for the $6k amount previously discussed here. One of their suggestions was to deposit $1k/month in sibling E's account for four months instead of a lump sum which would likely disappear very quickly. I'm of two minds there, one I'd like to just be done with it, but on the other, I'd be assured that my sibling had a roof over their head for the next several months.