Federal Parliament's "citizenship seven" will finally go before the High Court this week, for three days of public hearings. The court's decision - expected within weeks - could result in string of disqualifications, a NSW byelection and further chaos for the Turnbull government.
Joyce inherited New Zealand citizenship from his father. He has refused to step aside from his roles in cabinet, including as Deputy Prime Minister.
What happens if he is disqualified? A byelection in Joyce's northern NSW seat of New England. Joyce would be favourite to retain the seat, even if former MP Tony Windsor was to throw his hat in the ring again - but no unpopular government likes a byelection.
The deputy Nationals leader discovered she was a UK citizen by descent because her father was born in Scotland. Like Joyce, she has refused to step aside from cabinet.
What happens if she is disqualified? This would be messy. Because of the way the Coalition's NSW Senate ticket is formulated, Nash's seat would go to a Liberal: disability advocate Hollie Hughes. That could have knock-on effects for the Coalition agreement and numbers in cabinet.
Despite his initial claims that his mother had signed him up for Italian citizenship a few years ago, it turns out Canavan has actually been Italian since he was two.
What happens if he is disqualified? That would likely spell the end of Canavan's parliamentary career, at least for now. A High Court countback would elect former senator Joanna Lindgren. She's a Liberal but under Queensland LNP rules would sit in the Nationals' party room.
Xenophon was given British citizenship through his father, who was born in Cyprus when it was still a British colony.
What happens if he is disqualified? Xenophon will leave the Senate regardless of the court's decision, to run for a South Australian seat. If he's ruled ineligible his seat would go to Tim Storer, the next on his party's ticket. If not, his vacancy could go to anyone the party chooses.
Waters did not realise she was a Canadian dual citizen despite being born there and migrating to Australia as a baby.
What happens if she is disqualified? Waters has already resigned from the Senate. If she is found to have been ineligible, the seat could go to former Democrat Andrew Bartlett - provided he wants it. If she is found to have been eligible, she could potentially return to the Senate.
Ludlam was the first domino to fall, after he discovered he was a New Zealand dual citizen.
What happens if he is disqualified? Like Waters, Ludlam has already resigned from the Senate. But Ludlam appears to have no desire to return to Senate, paving the way for the next on the ticket - 22-year-old disability advocate Jordon Steele-John - to take up the seat.
Roberts was born in India to a Welsh father and didn't renounce his British ties until five months after he entered the Senate.
What happens if he is disqualified? Roberts is considered the least likely to survive: he knew there was a good chance he was British but he did not renounce. If he does survive, he'll stay in Parliament. If not, his seat will go to Queensland publican Fraser Anning, the next candidate on the One Nation ticket.