Just saw this thread title and did not understand what Jonah meant. So I looked up Jonah and found a definition that means a bringer of bad luck. Well, I've never heard that before. And then I read my first post on this page... it seems fairly irrelevant to the OP.
I don't see either Catelyn nor Cersei as harbingers of bad luck. I think they both do bring harm to those around them, especially to their children due to extremely poor choices. Both have their egos directly tied to their last thoughts. Whatever their last thoughts were, they refuse to be proven wrong. If both could stop and count to ten before responding... or wait a day or two while thinking things over, then maybe they would not be so short sighted.
Since we have more POVs for Catelyn, I'll user her an an example... Her first idea on Eddard being Hand is that it's a grand honor. They'll all go live in a warm climate with the Great Sept of Baelor close by. Her boys will be knights and her girls will be ladies. But she pushes back at Eddard's desire to refuse Robert.
After Bran's fall, Catelyn thinks they must all stay at Winterfell and cannot understand that Eddard has already committed to Robert and must now follow through.
When she wakes after battling the assassin, she knows she must be strong. She correctly deduces the Lannisters wanted Bran dead, but decides her strength must go to King's Landing instead of guiding Robb, watching over Bran and nurturing Rickon.
Arriving at King's Landing, she promises one silver to each sailor. The captain says he'll hold it for the men when Catelyn says she'll hand them out personally. Feeling unpaid, the captain immediately sells her location to Varys.
At the crossroads inn, she looks around and sees many armed men going to the Hand's tourney. She sees northmen, rivermen, Freys, families loyal to the Tullys, families loyal to the Targaryens, and a number of sellswords... and she thinks that war must be avoided at all costs. Five minutes later, she asks for loyal men, of Robert I and her father Lord Tully, to arrest Tyrion and bring him to justice.
When she joins Robb at Moat Cailin, she is worried about a fifteen year old leading an army. She also knows there needs to always be a stark in Winterfell, she knows Bran and Rickon need her, and she knows Eddard told her to stay in Winterfell. So instead of returning to Winterfell with Robb (letting a northman lead the army), she and Robb ride to Riverrun.
Catelyn's negotiations with Walder Frey were ruinous.
She coerced a drunken oath from the man with the worst reputation (and the deadliest sword) in Westeros and sent him under the protection of a woman, fully knowing this was treason, on a mission with a small chance of success in hopes of freeing one daughter (mayhaps two) upon the rumored promise of the Imp working for the King and Regent who executed her husband. She did this because she received news of Bran's and Rickon's deaths at the hands of the very man Eddard told her to keep close at hand. All she did was free up Tywin to scheme away and took away her son's one bargaining chip. Not a good plan.
What about Cersei?
She let herself continue a childhood game of naked 'Come into My Castle' with her brother for twenty-five years! This incest resulted in three children and led Stannis, Jon Arryn, and Eddard to learn her secret. This undeniable crime shattered her relationship with her father, her father's relationship with Jaime, he relationship with Kevan, destroyed Lancel's self worth, .... and could be seen as the primary cause of the War of the Five Kings.
In order to keep the prophecy of marrying the king a secret, she murdered her companion Melara.
She never disciplined Joffrey. She taught him to be arrogant. Readers knew Joffrey would not live long.
Cersei cowed and brow beat Myrcella and Tommen. Small wonder they immediately bonded with their fiancees and families to be.
The alliance with the Tyrells is the military coalition that proved insurmountable to Stannis, to Robb, and scared off Balon, Lysa and Doran. To fprtify this alliance, Tywin engaged Joffrey to Margaery, gave Loras a White Cloak, gave the Florent's lands to Garlan, gave the Redwyne's a tax break and wanted Cersei to marry Willas. Upon Tywin's death, Cersei snubbed Mace as Hand, snubbed Redwyne as Admiral, refused Willas, conspired to get Margaery arrested for treason, sent Loras to an almost certain death, had the Redwynne twins arrested for treason, and accepted Taena Merryweather (a Tyrell spy) as her closest confidant.
She refused her uncle Kevan's advice to continue his policies.
Needing money, she refused payment to the Iron Bank. The Iron Bank then cut a deal to back Stannis.
Still needing money, she negotiated with the High Septon for the Faith to forgive the Crown's debt so that the militant religious orders of the Suns and the Stars could be reformed.
She used this saved money to build a new fleet under the leadership of Aurane Waters, the ******* of Driftmark.
The upshot of all of this was that she herself was arrested and held by the reformed and revitalized Faith Militant for treason. Mace became Hand. Kevan became Regent. Margaery and the Redwynne twins were freed. Cersei had to do the walk of shame and is still waiting upon her trial by combat for high treason.
I think much of the mess surrounding their families is not due to chance, luck, happenstance, fortune, fluke circumstances, nor fate. I think it's due to foolishness, conceit and pride.