I wonder if having a "overload" plan in place that could be clearly "written up" and discussed with Mom and family. Kind of like a management plan for diabetes or asthma. You wouldn't tell your asthmatic kid who was starting to wheeze to "just get a grip" nor can a kid flooded with neurotransmitter or cortisol can't really "turn it off" just like that. But perhaps if you create a 5 or 10 point scale of "arousal" with your kid and check in frequently during the day to say "what number are you at" and link the numbers with appropriate soothing interventions, then he eventually might be able to self advocate and articulate his needs and you could have a tool to say-"this is how we are going to handle this situation." Hope this helps! By the way, I have Lupus and the extra stress of spd at home is rough-I can relate to just not having the energy & responsiveness to deal as we would like some days. Hugs!
Sirena