How do I correct Dad's seizure first aid before he looks after my son?

Dad said, "If he has a fit, I'll hold him still and put a spoon in so he doesn't bite his tongue."

My eleven-year-old has epilepsy and a care team's seizure plan. Dad wants to look after him for an afternoon. He means to reassure me, but what he described is not the plan. [CDC seizure first-aid guidance says not to restrain movements or put anything in the person's mouth](https://www.cdc.gov/epilepsy/first-aid-for-seizures/index.html).

I told Dad we needed to go through the plan and get appropriate guidance before arranging the visit. He thinks I am rejecting decades of parenting experience.

My son heard enough to ask whether he would have to sit through another family talk about himself. I want Dad prepared, and I want my son involved in what he needs without making him an exhibit for the adults.

How would you organise that conversation so the unsafe idea is corrected clearly and the care arrangements are understood before he is left with Dad?