First I am glad to see "separated brethren" in that context. Separated from Catholicism, not the body of Christ.
I will dispute that Catholicism is the "one holy catholic church" because Biblically it seems the one holy body of Christ is made up of every born again saved believer in/on Jesus Christ. Probabaly including a lot of Catholics.
I have no problem with Catholics following all of their traditions and beliefs and rituals and being beholding to your pope, and it would be nice if Catholics gave the same grace and consideration to OTC's (Other Than Catholic's)
(There is a lot of Catholic proselytizing goin' on here...)
Regarding separated brethren, I think if you like your faith community, you can keep your faith community (assuming it has not apostasized from the doctrines it preserved from the one holy catholc church, ie., does not deny the council rulings in place before they separated).