potty training support

hi everyone! I am a home health preschool. SLP and I have one child whose primary language is Bengali. He is five years old, autistic and a gestalt language processor. mom is concerned that he poops in his diaper, but won’t tell her when he poops and just sits in his diaper. However, he is telling Mom when he has to pee by saying “pee.” She has a new baby on the way and is very concerned about this. I have used visuals such as creating a social story (not interested), toileting sequence, visual for “I need to poop” and “I need a diaper change” but neither have worked. Also watching preferred youtube videos (baby shark potty + super simple). I have also discussed interoception challenges, but am feeling lost on how to best support this family.

Does anyone have ideas?

TLDR: child says pee but doesn’t let mom know when he needs to poop, mom needs support