Welcome to BYC. I would test your 6-year old based on the symptoms of the two you lost, before you bring the younger ones in. I like this lab https://www.vetdna.com/about-us, because they do not have reporting requirements. Results go only to you. There is a good symptom checker here...
I agree with @Debbie292d. Also, the root cause could be what @Eggcessive says. It is highly unlikely her issue is related to food. I think her skin looks fungal. I think it is gleet. Do you have monistat? It would not hurt to try it.
Welcome to BYC. You will like it here. Many members are very generous with their experience and time. Thank you for the pictures. We like pictures here.
Welcome. I must admit, I had to look up squab. I do not have pigeon or bunny experience, but can speak about chickens. I like the coop size you are giving 6-hens. With chickens, space takes care of many issues. The 6-chickens need 2-3 nesting boxes, but will all want to lay in the same one...
Welcome. It is very wise of you to join before getting chickens. I wish I had. Pay attention to our consensus about pre-manufactured coops (they are bad), the amount of secure space (more is better), and security (1/2 inch hardware cloth is your best friend). Also, make sure your chicken...