The pair featured for their new side in a narrow 1-0 defeat to Gomora United during their season opener at TUT Stadium on Friday.
Both players had been free agents since leaving Gallants at the end of the 2024/25 campaign.
Nange, an experienced holding midfielder, joined Gallants last season following a brief spell with SuperSport United in 2023/24.
The Limpopo-born player is best remembered for his time at Kaizer Chiefs between 2021 and 2023, where he enjoyed his most productive season in 2021/22, making 24 league appearances and scoring twice.
His stay at Gallants, however, proved less fruitful, as he managed just 13 appearances across all competitions with a single goal to his name before moving on.
Mahlatsi also spent one season at Gallants after joining on a free transfer in July 2024. The former Chiefs attacker made 20 appearances, contributing one goal and an assist during his short stint.
Their arrival at Leicesterfield City brings valuable top-flight experience to the newly rebranded club, which recently acquired the PSL status of JDR Stars.
Both players will be expected to provide leadership and depth as the Gauteng-based side looks to make its mark in the highly competitive Motsepe Foundation Championship.