So if two Catholics leave the church…get married…divorce…and possibly remarry they can easily rejoin the Catholic church and receive communion because their marriage is considered invalid…
Not “considered invalid” but “is invalid”. A Catholic who attempts marriage outside the Church without dispensation doesn’t marry validly.
but two Catholic who marry in the church,divorce and remarry need an annulment or they can never receive communion.
Two Catholics who marry in the Church marry validly. Nothing but death can dissolve their marriage. If they divorce civilly and attempt to marry another person, they commit adultery.
They may have evidence that what appeared to be a valid marriage was not. If they do, they can submit that to the Church to investigate. If it turns out that what appeared to be a valid marriage was not, they are free to marry.
or two Protestants marry in a Protestant church…divorce and remarry but cannot become Catholic until they get an annulment…or even if they marry in a civil ceremony…divorce and remarry in another civil ceremony…and then want to become Catholic they still need an annulment because it’s still considered a valid marriage…
Non-Catholics who marry do so validly unless there is an impediment. Marriages that are between two baptized non-Catholics are also indissoluble until death. Therefore, unless they can prove an impediment or defect existed, they are not free to marry another. If they do so anyway, they too commit adultery.
If we are talking about one or both unbaptized individuals, then it is possible that they have a valid marriage but it is also possible that it can be dissolved via the Petrine or Pauline principle.
but the original Catholic couple who marry outside the church get a fast track back to communion because their marriage was invalid…
They can receive communion because they are not committing adultery. Divorce is not an impediment to communion for any Catholic. Remarriage is.
If they are married-divorced-remarried all outside the Church, they do have an impediment to communion jut as the others do. They would need to convalidate their current civil marriage first. Which would require establishing freedom to marry and then exchanging consent in Catholic form. If their first marriage was outside the Church, establishing freedom to marry is less complicated than someone whose first marriage has a presumption of validity.