Chicks are sneezing but nothing else, can it be allergies?

Hi there!! I have two 9 week old chicks that have been sneezing for 10 days now. One even has a ear infection, but thankfully that is getting better now. I've been giving them antibiotics and VetRX. Sometimes I wonder if it is allergies. We have them on the porch in a cage with pine shavings. We would like to put them out in the coop but have 2 older chickens and worry we will get them sick, however they do interact here and there with each other during the day (free range) so figured they would have gotten it by now but luckily they are still fine.

My questions are 1. could it be a allergy? 2. if it is a respiratory infection, how long would it be til its gone? 3. Should we wait longer to put the chickens in the same coop, even though the chicks will stay in the cage away from the bigger chicks? 4. Is there anything else I should be doing to help them?

Thanks in advance to anyone with advice!!