Let me post this reference before sharing.
...This brings us now to the relationship addressed in Jeremys question: what is the degree of consanguinity between two cousins? Well, lets imagine Cousin Jenny and Cousin Mike. Jennys mother, Beth, is the sister of Mikes father, David. The common ancestor(s) in this case is the parent(s) of Beth and David. If we count all the persons involved in this relationship, minus the common ancestor, we find four persons involved. So these two cousins who in our parlance are first cousins are related in the fourth degree of the collateral line.
So can Cousin Jenny validly marry Cousin Mike? Not according to canon 1091.2, which says marriages are invalid up to and including the fourth degree. First cousins, therefore, cannot marry in the Church.
What year this canon law was made?
If it is older then 10 years then my parents of 50 years marriage wouldn't be able to marry in church also my sister and cousin (10 years ago wouldn't be able to marry in church)
To clarify my father's father and my mother's mother are brother and sister. My sister's father and cousin's mother are sister and brother. They are all married in church
The current code of canon law was promulgated in 1983. The previous code, promulgated in 1917, counts the degrees differently (canon 96), and has a slightly different restriction (canon 1076). Both code absolutely prohibit marriage, even if there is doubt about the relationship, in the direct line or in the first degree collaterally (brother and sister). Dispensations may be granted for more distant relationships that are prohibited under cans 1091 (1983) or 1076 (1917).
One can't use specific situations like this as a guide to interpreting the law, as there could be information that is unknown to you (e.g., dispensations granted) or the person who performed the marriages may have either not known, misinterpreted, or ignored the law.
If I understand correctly, both situations involved first cousins marrying, which is invalid under either code. My recommendation would be for those involved to speak with a canon lawyer to determine what the options are. My guess is they could get a dispensation now, then have the marriage convalidated, if that is even required. But best to go to the experts. Keep in mind that many parish priests are not familiar with canon law and it is, unfortunately, not uncommon for them to either be misinformed or simply make things up on the fly.