Upvote:2
This is going to depend on circumstances. You may have a situation where one or both parties were baptized Catholic before the marriage, but were married outside the Church without permission. And, you may have a situation where the couple was married before either became Catholic.
In the scenario where a couple were married outside the Church despite one or both already having been baptized, Convalidation may be in order. This is a rite by which the marriage is made Sacramentally valid within the Church. This, however, would not preclude the couple from participating in parish life. They simply would not be permitted to receive the sacraments until the convalidation was completed.
In the scenario where a couple were both married naturally, prior to either's baptism, there is no reason why they should be barred from the full Catholic life, sacraments included. whichever of them wished to convert would need to attend RCIA and eventually receive the sacraments of initiation. After this, they could fully participate in parish life without issue.
Lastly, you may have the case of divorced and remarried Catholics. Here, I am assuming that the past marriage was never annulled. In this scenario, just as with the first, access to the sacraments would not be permitted. However, except where there is danger of scandal, other participation in parish life may be permitted. Catholics in this situation would need to receive an annulment prior to convalidation. Or, they could separate from their civil spouse, or, if the situation requires it, "live as brother and sister."