Jackson and Sothern were not involved in the World League 2 success in March but come into the 18-man panel, which includes 10 Ulster players.
Ireland will qualify for the 2018 World Cup if they finish in the top five in the 10-team tournament.
They will play South Africa, Belgium, Egypt and Germany in Group B.
"We are looking forward to World League in Johannesburg, the obvious goal for us is to qualify for the World Cup and finish as high as possible in the tournament," said Fulton.
"The selected team has a nice blend of youth and experience, and the whole squad has been working really hard to get to this point.
"The team is in a good place and we're looking forward to completing our preparation in South Africa next week."
The Irish go into the tournament as the fifth highest ranked side, indicating that a World Cup qualification spot is very much in reach.
The Green Machine face hosts South Africa in their opening game on 9 July while a trickier task awaits in the second fixture against world number five Belgium two days later.
Egypt follow after that before the pool stages conclude with a 15 July match against Germany, a side Ireland defeated 4-2 on Sunday to win the Hamburg Masters.
Ireland squad: David Harte (GK), Jamie Carr (GK), John Jackson, Jonathan Bell, Matthew Bell, Chris Cargo, Matthew Nelson, Alan Sothern, Eugene Magee, Neal Glassey, Shane O Donoghue, Sean Murray, John McKee, Paul Gleghorne, Jeremy Duncan, Conor Harte, Stuart Loughrey, Stephen Cole.
Ireland coach Craig Fulton has added experienced duo John Jackson and Alan Sothern to his squad for Hockey World League in Johannesburg next month.