Ervine injured his hamstring in the first ODI, while Williams, who replaced him for the second game, fractured his finger at training soon after the toss.
Tendai Chisoro and Tawanda Mupariwa, who were part of the ODI squad, were left out, while the uncapped offspinner Tapiwa Mufudza earned a call-up. Brian Chari and Tinotenda Mutombodzi, who last played an international game in late 2015, were also recalled, while Chamu Chibhabha, who last played T20Is in January, was picked following decent returns in the ODI series.
Chari, an opening batsman who is yet to play T20Is, impressed for Zimbabwe A in their home series against Bangladesh A in November last year, when he struck a century to secure a draw in the second four-day fixture. Mufudza, who made his franchise debut in 2011, picked up 15 wickets in 10 T20s for Mountaineers, with best figures of 5 for 20.
Eleven members who were part of Zimbabwe's World T20 campaign, in which they failed to qualify for the main round, were retained. Among the notable omissions were Tinashe Panyangara, out with a back injury, and Luke Jongwe. Having lost the ODI series 3-0, with poor batting in all games, Zimbabwe will be hoping for better results in a format in which they are currently 12th in the ICC rankings.
"We're not going to reflect too much on the one-dayers, we are just going to look to hit the ground running in T20s," Cremer said after the ODI series loss. "We're going to try our best to turn things around."
He hoped Zimbabwe, who are ranked below Afghanistan and Netherlands, would draw inspiration from their T20 win over India last year. "I think it's motivating enough that the last T20 we played against India here is the one we won," he said. "It's motivating enough knowing how it felt when we won the last time, how good the crowd was and how we enjoyed that. Guys are looking forward to doing well and obviously having a disappointing one-day series makes us even more motivated to do well in the T20."
Zimbabwe squad: Graeme Cremer (capt), Sikandar Raza, Brian Chari, Tendai Chatara, Chamu Chibhabha, Elton Chigumbura, Neville Madziva, Timycen Maruma, Hamilton Masakadza, Wellington Masakadza, Peter Moor, Tapiwa Mufudza, Tinotenda Mutombodzi, Richmond Mutumbami (wk), Taurai Muzarabani, Vusi Sibanda, Donald Tiripano, Malcolm Waller