More flexibility with stem directions and notehead sharing

I am writing a percussion sextet with some unique indications for mallets/techniques. I'm trying to use shared noteheads and stems going in different directions. I'm running into major troubles, where I can get it to work in one measure and not the next. I've given up trying in Musescore, and I just added the extra stems with apple preview.

Here's some screenshots of what I'm trying to do: