Right-back Iorfa has arrived for an undisclosed fee from Wolverhampton Wanderers while left-sided player Lazaar and attacking midfielder Aarons have joined on loan from Newcastle United until the end of the season.
England Under-21 international Iorfa was Steve Bruce’s first addition as Owls manager following his formal unveiling at a packed Hillsborough press conference on Thursday afternoon.
The 23-year-old, who has been at Molineux for eight years, made 93 appearances for Wolves. He scooped the club's Young Player of the Year in the 2015/16 season.
Iorfa, who can also operate at centre-half, spent time on loan at Ipswich Town last season, having struggled to nail down a regular starting spot at Molineux.
He has reportedly cost Wednesday £500,000.
Lazaar, meanwhile, kicked off his career with Varese in Italy before joining Serie A side Palermo in 2014.
The Morocco international moved to Tyneside in August 2016, featuring 10 times as Newcastle lifted the Championship title. The 27-year-old spent last season on loan with Italian top-flight team Benevento.
Like his teammate Lazaar, Aarons has also found game time hard to come by at Newcastle. The speedy winger, who made his pro debut for the Magpies against Manchester City in the Premier League during the 2014/15 season, was farmed out on loan to Czech team Slovan Liberec, having struggled to force his way into Rafa Benitez's plans.
Aarons, 23, was not included in either Newcastle's 25-man Premier League squad or the reserve-team list back in September.
Speaking after formally being introduced to the media as Sheffield Wednesday's new manager, Bruce told The Star he was keen to add extra pace to his team.
"You don’t have to be a rocket scientist to realise that we need an injection of pace and energy," he said. "We need a few more younger ones.
"It won’t happen overnight but that has to be ther aim. Get a team together with a mixture of experience and youth, and see it where it takes us.
"You need all of that to be successful. Fitness levels are huge. That is something we have struggled on, if you look at the injuries.
"We have to improve that because the Championship is relentless. You have to be as good physically as the Premier League. In the past, that was not the case.
"Now, the data shows they are as good. We will also need that little bit of luck and resilience. You also have to be able to roll up the sleeves on a cold night somewhere."