Jo May, lol, your post sure brings me back to the days... My daughter was TERRIFIED of falling into, or flushing the toilet. Took her years to get completely over it. I still remember--and will likely never forget--one incident when she was potty training. She pooped on the floor, and I had to clean it up. My partner was even worse... His mom left him and his twin in their bedroom as toddlers, I think they were supposed to be having a nap... She came back, it was all over EVERYWHERE. Both of them, the walls, the floor, the bed (probably knowing them the ceiling lol). They were playing in it. Oh, that poor woman. When my daughter was in preschool, one of her friends would use the toilet, but not to poo, so his mom was dealing with diapers... Last I heard, he had agreed to use the potty when he went into kindergarten... When he was 5. LOL.
Good luck, as you know, your youngest will do it eventually. But it is sure frustrating at the time, I remember feeling the same way. It is hard not to get into a power struggle with them over it, so easy to just fall into that... Then it becomes a "control" thing for them. Talk about being between a rock and a hard place as a parent. That's one thing they know for certain in their little world, that they, and only they, have control over. The only thing they know their--otherwise invincible, to their eyes--parent cannot do anything about. You can make them eat a carrot, you can make them go to bed, you can make them mind their manners, and say please and thank you, but you cannot make them poo. And the little so-and-so's, they know it. LOL. The joys of parenting young children. Not helped by overly smug relatives... It's not a race, they all have their own special temperaments and quirks. :)