Tank mates

my mother in law's friend bought two axies from a pet store. they were pretty big. they are sharing the tank with a painted turtle and a group of fire belly newts. I was just wondering what's the first thing you think could go wrong in this type of set up? I tried to tell her that its not good to house these animals together. I figured if I can prove to her through here that its not good

depending on the size of the tank, there could be an increase in waste being produced (axolotls produce a lot of waste) so that tank could actually be overstocked and becoming toxic. I would also guess that all the inhabitants could probably get a bit snappy with each other, especially at feeding time, so I wouldn't be surprised if anyone lost some bits (gills, limbs).
As a general rule, the only tank mates axolotls should have is other axolotls of the same size. I'm really not sure how bad things would get mixing all the inhabitants of that tank, but it's not something I would be comfortable with, which I can see is your position as well.
Perhaps some of the more experienced keepers will give some more specific advice, but have a look at the links and see what information you can use.
Caudata Culture Articles - Species Mixing Disasters
Axolotls - Requirements & Water Conditions in Captivity
Best of luck.