...
My roll suggestions weren't too different either, I'll add the difference, for more choices. Ryhim has an investigation of +6. +10 with advantage? No, but there isn't a chance that Ryhim's brain will fritz out and make it -10. Something for consideration; everything else looks solid.
...
With mental break down check. Result of 1 delivers a -10 to the check roll.
Result: SUCCESS!
Rolls
Sizhen Insight Check (DC 12) - (1d20+8)
(7) + 8 = 15
Sizhen Mental Stability Check - (1d10)
(2) = 2