Yes, so far as I know, both Principal and dependent get passport request at a time. However, your case is different, an ethical issue involved here. Let's see what others comment. Every problem has a solution when you're honest. So, don't worry, friend. Good luck!!!!
1. Until the dependent completes the medical and the DMP sends the results to the RMC then of course CHC won't request the passport. Note you will still have to add the child to your application, amend your and spouses applications, send a copy of the child's passport, pay the fee, wait for medical instructions for the child. Depending on when the principal applicant had their medical, they may require another one.