Were they to the vet already? The bleeding and bubbles could be a respiratory infection, but I'm not sure about the lumps. I have no experience with chytrid so I'm not aware of the symptoms. They are well beyond an internet diagnoses by the looks of it though.
Regardless of whether they've "always been fine until now" you need to make sure they're living in proper conditions. Environmental factors might not affect them short term, but can long term. You can't expect to have healthy frogs with a long life if you do not follow proper care for their species and they're not fine now.
Were the two new ones tested for parasites or fungal infections before you introduced them? Sometimes these things can lay dormant before attacking. They do need a lot more perches, tall branches, so they can claim their own space.
And honestly, dirty glass is better than a dead frog. You could get away with no substrate but only if you're measuring humidity and making sure it is correct for them.