Nope, never in the same tank. They weren't even in the house at the same time. I only have one tank, so I only keep one betta at a time.
I'd have more, but without a heavy unmoveable tank, my cats would cause complete and utter destruction.
It was really weird. She had been a little lethargic and slightly pale for about two days and then on Sunday morning when I woke up the loaches and ghost shrimp were having a feast on her. It must have just happened because she wasn't even stiff yet. I seriously doubt the loaches could have killed her - they just like to eat dead things. There was no cloudiness anywhere on her, she had no sores other than the hole where they had been feeding. Even her eyes were still clear. The tank parameters were perfect. Nothing new had happened other than the introduction of the now sick snail. And she was at most 6 months old. (I like buying the teeny-weeny baby-bettas.) I've had practically every disease a betta could get - (I usually buy "rescue" bettas) - but this was a complete shock.