The Sarr deal, first reported in these pages as a verbal agreement, is now understood to include a £25.7m obligation to buy at the end of the season - close to the €30m figure earlier reported in Italy.
Spurs have also given the green light for Moore's loan to Bundesliga side Köln to be finalised, while left-back Souza is heading to Porto on loan for the remainder of the campaign.
The outgoings come as Tottenham continue working on incomings, with the club still in talks with Everton over Iliman Ndiaye, who has turned down multiple contract offers from the Merseyside club over the past year.
In a related move, Everton are separately working to bring Richarlison back to Goodison Park - part of the same wave of departures Roberto De Zerbi confirmed after Saturday's 2-0 defeat at Newcastle, when he revealed that Richarlison, Sarr and Kevin Danso had all asked to leave before the deadline. Danso has attracted loan interest from Sunderland.
De Zerbi made clear afterwards that no player determined to leave would be stood in the way of, provided the financial terms worked for the club.
"I love these players, they are great guys, I have very good relationships, but if they want to leave, they have to bring the solution, the economic solution, to the club, and they can go, and we find other players," he said.
With Sarr, Moore and Souza all now departing and Danso's future still to be resolved, Tottenham's priority for the closing hours of the window remains completing a move for Ndiaye or an alternative forward to freshen up the squad before deadline day.
Moore's loan to Köln offers the 18-year-old winger regular senior football away from a crowded Tottenham forward line, having made only sporadic first-team appearances since breaking through last season, while Souza's move to Porto continues the pattern of fringe players being sent out for experience as De Zerbi trims his squad to a more manageable size.
Between the confirmed exits and the ongoing pursuit of Ndiaye, Tottenham's business over the closing 48 hours looks set to reshape significant parts of the squad De Zerbi inherited at the start of the summer.