The High Court has named three new senators to replace ousted dual citizens but a question mark remains over the fourth.

The three confirmed senators will be sworn in on Monday, but doubt remains over NSW Liberal Hollie Hughes, who was next on the ticket after NSW National Fiona Nash.

On Friday, the court declared the winners of a special count by the Australian Electoral Commission to replace former senators Malcolm Roberts, Larissa Waters, Scott Ludlam and Fiona Nash.

All four were disqualified from Parliament due to their dual citizenship.

Former Australian Democrats leader Andrew Bartlett will return to the upper house, replacing Ms Waters as Greens senator for Queensland.

Business consultant Fraser Anning will step into the Queensland One Nation seat vacated by Mr Roberts.

And 23-year-old student Jordon Steele-John will replace Mr Ludlam as Greens senator for Western Australia.

High Court Justice Stephen Gageler said the Full Court should consider whether Ms Hughes is eligible to replace former deputy Nationals leader Ms Nash in the Senate.

The Senate recount was ordered because Ms Nash was disqualified from the Upper House as she was a dual citizen at the time of the last election.

There are questions over whether Ms Hughes can take up the position, because she worked at the Administrative Appeals Tribunal (AAT) between losing the election and the Senate recount.

Another section of the constitution bans people from holding parliamentary office if they also held an “office of profit under the crown”.

That prohibits public servants from running for office.

Ms Hughes resigned from the AAT before the recount.

The matter will be dealt with next Wednesday, the same day that the same-sex marriage survey result will be announced.

The three confirmed senators will be sworn in on Monday ahead of the Senate voting on a new president to replace Liberal Stephen Parry, who resigned over his dual citizenship.

The position is tipped to go to Special Minister of State Scott Ryan.

– AAP, ABC