@apollo Hi Kris,
I have few questions:
What is timing of your project? (tasks and MbDrv)
Can you record and share a log with settings from the following post?
(from the log you will also get an idea how the MbDrv sequencing works which might help you to improve the settings)
Let me answer your question about registers order: Yes, it would make sense to mix the slaves. The order matter with respect to the same "Period" settings. (MbDrv works as a priority queue)
Thanks for cooperation.