I did make the time today to check on one item in your post, the reference to the death of Chief Wryneck in the Virginia State Papers. That reference, to my mind, settles the question of whether Joshua Renick was Moluntha. Clearly he was not.
I refer to "Calendar of Virginia State Papers," ed. Wm. P. Palmer, Vol. III (Richmond, 1883), pp. 565-566. On 2 March 1784, a speech from the Shawnees and Wyandots to the Governor and Council of Virginia was signed by White Wolf, Peniwesica, and Millonthy (Moluntha). On the same day, apparently enclosed, was a separate message signed byKekipeletha, Pupscullalo, and Potheca, who explained,
"Brothers, We are But a few young Men that now sends you this Talk, for our nation, as our Great Chief Rynack, was taken from us by Death. Before he could finish the Business."
Your argument that Spemica Lawbe (James Logan) was adopted by Molunthais clearly consistent with the death date of Rynack/Wryneck, and fills the logical gap between this evidence and Lytle's account which names Moluntha as Logan's father.
This is fascinating stuff. Thanks for posting your research. I'll work on my end of it, as you suggested.