You have referenced this document several times and the last paragraph is interesting, “12. Finally, it must also be borne in mind that the expression sister Churches in the proper sense, as attested by the common Tradition of East and West, may only be used for those ecclesial communities that have preserved a valid Episcopate and Eucharist.”
So a sister Church is one who’s “ecclesial communities have preserved a valid Episcopate and Eucharist.” Let’s look at the Second Vatican Councils Decree on Ecumenism, Unitatis Redintegratio, “These Churches, although separated from us, possess true sacraments, above all by apostolic succession, the priesthood and the Eucharist, whereby they are linked with us in closest intimacy. Therefore some worship in common (communicatio in sacris), given suitable circumstances and the approval of Church authority, is not only possible but to be encouraged.”
This Decree on Ecumenism states that the Churches of the East who are not in communion with Rome possess “apostolic succession” and “the Eucharist.” According to the document you referenced, what make a Church a sister Church(?), " . . . those ecclesial communities that have preserved a valid Episcopate and Eucharist."