@Saaniya is also in India, and knows what medications are available. Respiratory infections can be from a virus such as infectious bronchitis, ILT (infectious laryngo tracheitis,) or bacterial or bacteria-like, as in mycoplasma (MG,) or coryza. Newcastles is another much more severe disease that is common in some parts of the world.
Antibiotics such as Baytril (enrofloxicin,) tylosin, tiamulin, and oxytetracycline can treat MG, and sulfa antibiotics such as sulfamethazine and others may treat coryza.
If you are just seeing sneezing and a slight nasal drainage, it may be a virus which does not respond to antibiotics. But MG can look similar if it is a mild strain. If there is thick mucus, eye bubbles, wheezing, or facial swelling, I would use antibiotics if you keep the birds. Most respiratory diseases make survivors and the other birds carriers, sometimes for life. Sorry that you brought in sick birds. Sometimes stress will cause them to get sick.