Thanks for more information and pictures.
I'm not a veterinarian, and with any issues with parrots an avian veterinarian should be consulted. I'm quick to turn to my avian veterinarian and they have saved my birds.
We have to talk about diet. The food you are providing is not nutritionally complete. Birds that have reached 2 years have burned through the liver stores of some vitamins they were born with. Notable vitamin A. Your diet of seed and corn isn't proving vitamin A and many other key vitamins and minerals. Those missing nutrients play a key role in health and immunity. So this is a age you can start seeing a big decline in health , upto loss of life from nutritional deficiency.
So changes have to made to diet , it can take effort and patience to get them eating better. I think I saw sticky thread to offer help with diet change. But some foods rich in vitamin A/beta carotene are peppers, sweet potatoes, carrots, romaine lettuce. Parrots usually take to peppers pretty easy , sweet ones and hot ones, even dried peppers are still a source if vitamin A which is why they are included in many parrots seed mixes. Offer the deep Yellow/orange/red bell pepper they can eat the seed too. Cooked sweeet potatoes mashedd and served warm are often taken too quickly, butter nut squash , and pumpkin. Try serving shredded carrots. Cooking carrots also makes the vitamin A more bio available. Romaine lettuce is actually a good source. Birds will often nibble this pretty early on in diet changes. Serve whole leaves, hang them, weave in cage bars. I'm focusing on vitamin A rich foods because they are so critical and seed have none.
Part of your birds poop problems are linked to diet, that's safe to say even as a non veterinarian. They can be having fatty liver and a host of other nutritional disorders effecting their internal organs. Because key nutrients are missing.
Diet effects immunity. Decreasing their ability to fight off infection.
With these poop pictures we are seeing clay colored stool, Cloudy urine, some bile acid stained urine ( dark green) strings of urates or no urates, and increased urine ( the wet part. )
I think this is nutritional plus bacteria infection, likely chlamydia. Its definitely nutritional plus something( bacteria/fungal/viral).
Diet change plus seek veterinarian. A veterinarian is warranted and needed, they can determine cause and provide medicne