I haven't seen a post from you for awhile and am heartbroken to learn that after everything you have tried you are feeling worse

I have heard of a patient who had the S-T ligament severed by the Houston team with negative consequences, having the ligaments repaired after the fact by a general Orthopedic Surgeon. Maybe you could pursue that with the SS ligaments if you have a high degree of certainty that this is causing pelvic instability.
As you know from prior threads I am adamantly against cutting the S-T ligament; but I see the role of the SS as lesser. Are you sure this is the cause of your SIJD? When I had SIJD, I had a high degree of pelvic instability (hypermobility); but it self-corrected when the HYPOmobilities (stuck joints) within the pelvis were released. I wonder if hypomobilities might be an alternative explanation for your pelvic instability, because the SS ligament is a relatively minor player in pelvic stability.
Again, I am so sorry that you haven't yet found the help you have been looking for. You are a very well informed patient self advocate and I know you really did your homework in pursuing a cure. You deserve better.