A few questions about your crested geckos.
1. Are all of these from the same breeder?
2. What temps and humidity levels were/are they being kept at?
3. What are you feeding and how often?
4. Are your cresteds a special morph?
5. How much are you handling?
Answer these for me and maybe we can help at least eliminate a few possibilities. To my knowledge, IBD isn't common or present at all in geckos but I don't have any experience with the disease myself, so won't say for sure that that's not a possibility. MBD however can present with what could appear to a newer keeper as neurological issues. With crested geckos stress can cause immune issues which can lead to all sorts of issues, dehydration or too much humidity can cause some of the issues you described as well. Lastly poison is a posibility for sure. We have a cleaning service come through once a month and unfortunatly I wasn't here to keep them out of my office where the animals are. I lost a crested gecko to cleaner, but fortunatly everyone else was fine.
At the end of the day if you're seeing similar symptoms in your snakes that you saw in your geckos, don't wait for us, a visit to a vet that specializes in reptiles may be called for.