The four, including the former secretary-general of the ruling party Pagan Amum, were released from detention last month, but President Salva Kiir initially banned them from travel abroad.
However, Kenyan President Uhuru Kenyatta met with the four on Thursday in Nairobi.
“The detainees… were released and handed over to him last week,” the presidency said in a statement, adding it was “a first step” in reconciliation.
The three other freed detainees are ex-national security minister Oyai Deng Ajak, former ambassador to the US Ezekiel Lol Gatkuoth, and ex-deputy defence minister Majak D’Agoot.
The four were the last of 11 leaders held after being arrested in Juba in December when fighting broke out between members of the presidential guard. The other seven were freed and handed over to Kenya in January.
The fighting rapidly escalated into all-out war between troops loyal to Kiir and defectors and ethnic militia loyal to sacked vice president Riek Machar.
Kiir accused Machar and his allies of attempting a coup, but the rebel chief denied the allegation, and in turn has branded Kiir a “genocidal leader” who started the war by carrying out a purge.
Charges remain against Machar, who fled the capital and is leading the rebellion, as well as other two key rebels, former governor of the oil-rich Unity state Taban Deng, and ex-minister Alfred Ladu Gore.
Kenyatta said the release of the four men was a “step in the right direction” towards peace, but stressed the need for talks between Kiir and Machar to go ahead as soon as possible.
The leaders are due to meet for talks set for Friday in Ethiopia, although Machar has already said he will likely not reach Addis Ababa in time.
“We need to move quickly… to the next phase of a face-to-face dialogue between President Salva Kiir and Riek Machar,” the statement added.