Well, to stay with the USA there is Tec, acna and dozens of continuing Anglican churches; and another dozen of churches that call themselves Episcopal church, but are in neither of mentioned church bodies (like the charismatic Episcopal church). I guess I haven't really understood which of these are in the worldwide Anglican communion and which not and which are really apostolic churches (in case of the various Episcopal churches outside Tec).
I had the feeling this wasn't quite clear in your mind yet.
TEC is the official representative of the Anglican Communion in the USA. No other Anglican church is. However, ACNA is trying to persuade the Anglican Communion to make it the second recognized province here and has the official recognition of a number of overseas churches that are members of the Anglican Communion. (I doubt that that will succeed.) The Continuing Anglican churches are not desirous of joining the Anglican Communion.
Imo, it's getting even more confusing when you have a look why they left Tec (which is as far as I have understood it the official Anglican church of the USA in the worldwide Anglican communion). And much more confusing when it comes to the theological differences. - Which ones are those that came back to the rcc (although that was the UK, if I remember correctly.)?
This is something that should NOT be all that confusing. First, the Continuing Anglican churches left TEC (and the ACofCanada) because of two issues: the ordination of women and (in their view) the severing of Apostolic Succession, and also the reworking of the Book of Common Prayer to make it more liberal theologically and more of a collection of liturgies than anything "common."
ACNA (also called "Anglican Realignment") left over TEC's acceptance of the main demands of the homosexual activists: gay bishops and priests and, secondarily, same-sex blessings and unions.
Both the Continuers and ACNA were generally alarmed at the liberal drift of The Episcopal Church, it should be added. However, that's less easy to itemize or summarize.
As for the Anglicans who went over to the the RCC, they number only a miniscule number, maybe a couple thousand, and are mainly in the UK, although there are some in the USA and Canada.
So you think Tec would cease to exist some time?
Probably not. But it is losing about 1,000 member each week and has been forced to close and/or sell off a growing number of church buildings and properties. Few dioceses have averted serious shortfalls in meeting their budgets. The situation is worse with the Anglican Church of Canada which is more likely to actually cease to exist.
why they split from the Anglican church in Canada?
The same reasons as ACNA in the United States.