Despite my lack of knowledge of the canons, I have read a good deal about the debate between the Patriarchate of Moscow and the Ecumenical Patriarchate just prior to and after Moscow issued its Tomos of autocephaly as to the OCA. The reason why we can even engage in this debate is that there is not a canon that defines how autocephaly is achieved. Both Churches agreed that the future Holy and Great Synod (Council) would be the final determiner of the OCA's autocephaly.
I don't want to reactivate the debate, because far too much has been said by both sides of the OCA autocephaly issue, without resolution, which stymied any unity efforts for North America over the past 38 years, but out of love for the holiness of the Metropolia, communion may not have been broken, but that doesn't negate the fact that only all but two of the Holy Orthodox Churches had officially accepted the OCA's autocephaly, primarily because, in part, of the multiple diocesan entity's that it overlaps. Twenty one or so years after the Tomos was issued, the Ecumenical Patriarchate officially recognized the OCA's ability to govern itself and elect its own hierarchy, including its primate, but did not accept its claim to autocephaly. I would submit too, that the Moscow Patriarchate tacitly acknowledged that their autocephaly plan didn't quite work, by agreeing to the Episcopal Assemblies plan for the territories, including North and Central America, that are not within the boundaries of the Holy Orthodox Churches.
The point herein is that it does seem that a part of the process toward autocephaly, includes whether the sister Churches agree to accept a new member of the family of our Churches.