I'm new in town, and it's a delight to follow your discussions!
On free will:
I'm inclined to doubt that free will as usually conceived is a coherent
idea. On the one hand, 'freedom', as a property pertaining to alterations
of mental states, connotes a mysterious suspension of causal influence from
the rest of the world. On the other hand, however, few would accept an
analysis in terms of _randomly_ engendered alterations.
It is perhaps more instructive to understand free will in terms of
downwards causation. Mental states are higher-level features of certain
machines such as brains, by (very rough) analogy with liquidity being a
higher-lever feature of H2O molecules in motion. Some of these states have
in turn a causal impact on
constitutive elements on the lower level (e.g. neuronal firing patterns).
This dwe might think of as "free will". On this analysis, the distinction
between the 1. and 3. person perspectives is purely epistemic: The
panscient spectator would have no use for it.
But I fail to see any special connection between free will, however
understood, and the multiversum models - pace e.g. Deutsch in "Fabric of
Reality". Maybe a multiversum view is required for a coherent analysis of
counterfactuals, hence of causality, and hence of downwards causation; but
that's a much more general matter.