West Indies all-rounder Kieron Pollard and Australian fast bowler Jhye Richardson will play for Welsh Fire in the Hundred franchise tournament.
They replace Australian pair Steve Smith and Mitchell Starc, who opted out of this year's event.
Glamorgan vice-captain David Lloyd has also been picked.
Australian star trio Meg Lanning, Beth Mooney and Jess Jonassen are retained by Welsh Fire women, with all fixtures being staged as double-headers.
Glamorgan's Colin Ingram will now play as an overseas selection for Oval Invincibles, after being named in the Welsh Fire squad as a "local hero" in 2020, while fast bowler Timm van der Gugten is with Trent Rockets.
But Welsh Fire had to change eight of their 15-man squad because of alterations in availability and eligibility from the inaugural tournament in 2020, which fell victim to coronavirus restrictions.
They had the second and seventh picks in the revised draft, with West Indies limited-overs captain Pollard, 33, top of their list.
He has made 189 international appearances in white-ball cricket, is about to play for Mumbai Indians in the Indian Premier League, and has played county cricket for Somerset.
Western Australia paceman Richardson, 24, was the top wicket-taker in Australia's Big Bash and stands to earn nearly £1.4 million playing for Punjab Kings in the 2021 IPL.
Afghan spinner Qais Ahmad was retained as the third overseas player, while England batsman Jonny Bairstow also returns.
Welsh Fire have also added Notts and England fast bowler Jake Ball, Gloucestershire batsman Ian Cockbain, Northants all-rounder Josh Cobb, and Derbyshire spinner Matt Critchley as well as Welsh all-rounder Lloyd.
Glamorgan captain Chris Cooke was earlier retained by Birmingham Phoenix.
Aussie trio remain
There is less change at the top of the Welsh Fire women's list, with current Australia captain Lanning, dubbed the "Megastar" of the sport there, happy to sign up for a second attempt at the new competition.
The 28 year old Victoria and Perth Scorchers batter is joined by two other vastly experienced stalwarts of the Australian side in wicket-keeper batter Mooney, 27, and spin-bowling all-rounder Jess Jonassen, 28.
"There was a little uncertainty but once we knew the tournament was up and running again and there was a lot of hard work put in, I was very keen to be involved," Lanning said of her decision to re-commit.
"It's going to be an exciting competition coming in and as players we want to be part of that. I had a chat with Jess and Beth, they're very experienced internationals and will be great additions to the Welsh Fire.
"I think it'll help that we know each other very well and gelling in the early stages of the tournament will be very important so hopefully it sets us up well," she told BBC Sport Wales.
They will be playing under Australian women's coach Matthew Mott, who was in charge at Glamorgan between 2011 and 2013.
"He said Cardiff is a very nice place and a great place to play cricket as well, so that played a role in getting us there and I look forward to meeting everybody," said Lanning.
Surrey batter Bryony Smith, who has made four appearances for England and featured in their 2020 squad without playing, is the latest addition to the domestic players.
Welsh all-rounder Alex Griffiths was confirmed earlier for the squad, but spinner Claire Nicholas misses this year for family reasons.
Both men's and women's teams will begin their campaign against Northern Superchargers at Headingley on Saturday 24 July.
The first of four home matches for each franchise at Sophia Gardens come three days later, when Welsh Fire take on Southampton-based Southern Brave.
South African Gary Kirsten is again due to coach the men's side.
Welsh Fire men: Ollie Pope, Kieron Pollard, Jonny Bairstow, Jhye Richardson, Tom Banton, Jake Ball, Ben Duckett, Ian Cockbain, Qais Ahmad, Josh Cobb, Liam Plunkett, David Payne, Ryan Higgins, Matt Critchley, David Lloyd.
Welsh Fire women: Meg Lanning, Beth Mooney, Jess Jonassen, Bryony Smith, Sophie Luff, Georgia Hennessey, Alex Griffiths, Lauren Filer, Amy Gordon, Nat Wraith, others TBC.