Non-Normality - Measuring of stereotypes

Hello :)

I'm researching a moderated mediation (2x2) with two mediators.
To test my MANOVA and moderated mediation I have to check the normality assumption of errors (residuals). My sample size is 400.

1.) One of my mediators has a non-normality distribution of residuals (which I think is logical, because I'm quantify attributions [stereotypes] of helpers) --> Do I have to transform my mediators? If so, do I have to transform all variables or only the affected variable?

2.) how do I test non-normality in SPSS? Do I have to put all variables?

My model:
IV 1: nominale scale
IV 2 (& moderator): nominale scale
Mediator 1: interval scale
Mediator 2: interval scale
DV 1: interval scale
DV2: interval scale