If you cast multiple blades and traps that are from the same "source", only one will trigger when you cast an applicable spell.
For example, if you cast a Mythblade spell that you have trained, a Mythblade gained from an item, and use a Mythblade treasure card, they will all trigger when you cast a Myth damage spell since they are from different sources.
Whereas if you cast two Mythblades from your deck, only one will trigger at a time when you cast a Myth damage spell.
I hope I was able to answer your question. Good luck!
No, but you can only cast one of the same exact blade/trap at one spell. For example, if I casted Death Blade and then Death Blade and then Avenging Fossils, it will only take one of my blades and not two. So nothing's wrong, you just need more blades for the selection.
On a similar note, make sure you cast prisms before school specific traps. If you cast a prism after your school trap the trap won't get used. Order doesn't matter with blades.
