Husband won’t potty train our 3.5 year old

I work 4 days a week and my husband is at home because he suffered an injury at work. He refuses to potty train our 3.5 year old.. he’s traditional so he doesn’t believe a man should be in charge of potty training. It’s super hard for me to because I’m at work most of the week and days I don’t have work, my husband takes us out for family outings, so it’s pretty much impossible. Does anyone have any tips on how to tackle this issue?

Oh and ps my mum offers EVERYDAY to potty train my son but my husband refuses because it’s my mum and he doesn’t respect our family. So there’s that.