"Members are assigned positions in the order of precedence, coming before all others of knightly rank, and above baronets. The wives, sons, daughters and daughters-in-law of Knights Companion are also assigned precedence. Relatives of Ladies Companion are not, however, assigned any special positions. (Generally, individuals can derive precedence from their fathers or husbands, but not from their wives.) The Chancellor is also assigned precedence, but since 1837 the office has been held by a diocesan bishop of the Church of England or a peer, who have a higher precedence than that bestowed by the Chancellorship.[43]"

This is something I found, yeah, it's Wiki, we know the Windsors have played fast and loose with protocol so we'll see how the protocol is set out.
I have a feeling that the Duchess of Cornwall will walk beside her husband, even if against protocol, Charles will insist.



https://en.wikipedia.org/wiki/Order_of_the_Garter