1. Who (as in what "level" of church) can issue, for lack of a better word, a tome of autocephaly/autonomy? And can that church do it unilaterally or does it have to
So prior to the current controversy, there were two positions: the Ecumenical Patriarchate held that the Church as a whole, either in council or in comparable mechanisms, grants autocephaly and it can't be done unilaterally. See, for example,
here and
here. Russia, on the other hand, held that a mother church (not in the sense of 'the church that historically evangelized an area', but rather in the more precise canonical sense of the church on whose holy synod a given group of bishops sit) could grant autocephaly more or less unilaterally, pending wider recognition, as was the case with the OCA. They both agreed, in preparation for the 2016 Council of Crete, to a
document that made it a decision for the entire Church, coordinated by both the Patriarchate of Constantinople and the mother church. They disagreed, however, about the manner in which a tomos of autocephaly should be signed: Constantinople wanted its signature at the top alone, while Moscow insisted that the signature of Constantinople and the mother church be side by side. This sounds petty, but Constantinople has a history of trying to use interpretations of symbolic gestures to make substantial ecclesiological claims, so most of the other churches are careful about this sort of thing now. In the event, the document was scrapped due to lack of agreement well before it was announced that four churches would not participate at Crete. Constantinople, however, used this lack of agreement as a chance to drastically revise its own understanding of how autocephaly should be granted.
2. how is the situation with the Ukrainian Orthodox Church different from that of, say, the Bulgarian Exarchate from like 1872 to 1945?
In the case of Bulgaria, the Bulgarian bishops who unilaterally proclaimed their own autocephaly had been canonical bishops of the Patriarchate of Constantinople, which condemned them in a council where the patriarchs of Alexandria and Antioch also agreed (and that of Jerusalem, oddly, did not). This condemnation was not, however universally recognized, and the Bulgarians received tacit support from Russia and the Romanians. In the case of the current 'autocephalous' Orthodox Church of Ukraine, there are three sources of bishops: 1) those who had been part of the Kiev Patriarchate, whose leadership was anathematized and excommunicated by Moscow--- an act, crucially, recognized by the Patriarchate of Constantinople: see
here and
here. 2) the so-called Ukrainian Autocephalous Orthodox Church, whose bishops have
extremely dubious apostolic succession. 3) Two bishops, of which one was an auxiliary, from the canonical Ukrainian Orthodox Church. So, there are two major differences between the Bulgarian and Ukrainian situations: 1) While in Bulgaria all the bishops were originally canonical and only a tiny minority rejected autocephaly to stay with Constantinople, in Ukraine the vast majority of canonical bishops rejected autocephally granted by a third-party church. 2) The existence of the bishops in the new Ukrainian church whose very ordinations are of dubious validity. Additionally, it is difficult to understand how the Patriarchate of Constantinople can renege on having twice recognized Moscow's "exclusive competence" to excommunicate and anathematize Filaret, the leader of the Kiev Patriarchate.
Who are these "Ucrainicans"?
This is just Isa's joking way to refer to the Orthodox Church of Ukraine, implying that they are analogous to Anglicans as a nationalistically-motivated movement.