Who provides the umpires in Stage 2, and which team supplies the square leg umpire?

Each team provides one competent umpire when required (General Rules 3.1). In Stage 2:

Where a team has no association umpire, it should supply a volunteer to umpire at square leg or for half the match.

Stage 3 differs: with no appointed umpire, the batting team supplies the central umpire and the bowling team the square leg umpire.

The Laws of Cricket apply wherever the MJCC Stage 2 Match Day Rules are silent.