Actually...certain illnesses can take several weeks to show up. Hence the 30 day quarantine. The toxins in the skin can lead to a very very slow death for these frogs, they might seem fine for a while, but after being housed together for a time, things can happen. A month and a half is nothing.

The pet store you got them from was just downright stupid. Those species should not be housed together.

It's not just how they interact with each other, but that they all have different types of needs too. A firebelly toad and an american toad and a tree frog for instance, they all need different levels of humidity, different temps, etc. You are going to stress these frogs and toads out and they are all going to die over time. You will be devastated in 6 months when one by one your animals start dying off. Take the advice of the experts in this forum. They know what they are talking about, they know 100x's more of what they are talking about than most pet store workers!

I have only been keeping for a month now and I would trust their knowledge far more than other resources.