Paul,
To put this as simply as possible; unless they're actually capable of killing it, no fish can out-aggressive a piranha. So you've either doomed the piranha or you've doomed the other two.
Your profile shows that you have three tanks, all of which are absolute disasters. A 30g tank with two large, aggressive fish and one large, aggressive, piscovorous fish. A 10g tank with a newt and a crayfish (which will eventually decide to eat the newt, and produces far too much waste for a 10g tank), but the worst of all of them is the little
betta kit with three bettas in it.
I'm nearly positive I've suggested this before, and I promise that this is the last time I'm going to say it, but it needs to be said:
Take all of your fish and inverts back or give them to friends. Keep the 10g with only the newt in it, or take the newt back and put
one of the bettas in it. Stock the 30g with small fish that do well in a 30g. Throw the betta kit away, or use it as a flower vase. No fish belongs in it.
If you don't, and if you keep replacing your dying fish with other inappropriate fish, your fish will keep dying. You will be wasting money, which is bad enough, but you'll also be killing creatures whose only crime was to be put into the aquarium trade.
You have decided to keep these creatures as pets. They had no choice in the matter. It is your responsibility to provide them with the proper circumstances to not only survive, but to
thrive.
You're starting in the aquarium hobby early (many of us didn't really start until we were quite a bit older), and have the chance to learn more about the hobby than many of us ever will. But first, you have to start learning. It's okay to make mistakes; we all do; but you have to
learn from them and strive not to repeat them. If you let us help, and take our most basic advice, you will begin to learn in leaps and bounds, and by the time you're my age, you could easily be working with the aquariums at the local zoo, or working as a marine biologist at a university, or any number of related jobs.
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They are also big waste producers and in a bowl they WILL die of 
Research is a great tool and you should do more of it before purchasing fish. I know that fish are pretty and neat to watch but they are also living creatures and it's it's actually heart breaking for me to read this thread. 
it was cool watching him eat them. I also have a newt!!!!! btw ive finally got the fish to come out of the rocks. its a massive ruby shark! ive gotten him sent to the fish store to be checked out hes about 2. its because my friend when he took care of my fish for a week he added it in without telling me then he told me just recently. but im keeping him. hes not that agressive. also my 
is all I have to say paul....I really hope all your fish survive...goodluck!
I'm done.
I would read the advice from Ken and Sir above and follow it. 
Pirahanas really need to be in a species only tank and they do best when they are with other pirahanas instead of just 1. A pirahana can NOT be in a community tank, even if your other fish are "very very aggressive" I'm starting to wonder if you even read any of the other posts from other members that are trying to give you advice. I think a little bit of research would go a long way for you.
