Church of Christ subsists in the Catholic Church. Actual Members of the Church are the subsistent core, while also in the Church you can find various Hindus, Muslims, heretics, and schismatics. Sounds like a profound explanation of this reality. Check.
We have "separated brethren". Indeed Hindus and Muslims and heretics and schismatics are separated from us (because they do not share the Sacraments nor profess the faith) but they are brethren because they are within the Church. Check.
Ecumenism. We're no longer talking about conversion but of coming into a greater fullness of truth. Conversion is no longer binary. Indeed if Hindus, Muslims, heretics, and schismatics are in the Church, it's not truly a question of "converting" them because they're already within the Church, but of opening their eyes to the full truth of Catholicism. Check.
Religious Liberty. Since doing the will of God and following your conscience and your lights (even if erroneous) pleases God and is salvific, and since everyone has an objective right to please God and save his soul, then everyone has an objective right to follow his conscience and his lights (even if erroneous). Check.