Oh we are in the same situation exept that my husband do not have any contact with the mother and the child. We send the declaration that we will not have his son examined/sponsor on dec 30 ( they ask for medical for his son in the AIP that we received dec 20 ). So your saying it can take FEW months before receiving the letter from IRCC that we'll have to sign ? How many months in your case ?We were in the same position. When we completed my husbands medical, I sent a letter to the VO along with a copy of my text messages with the mother who refused to have her child do the medical and the receipt confirming we completed my husbands medical. A few months later they sent me their version of the statutory declaration. We had to sign their form confirming we understood we could never sponsor the child in the future.
I think our reprensent make a big mistake here. In august IRCC asked us to add his son in the IMM0008 even if he never met him and have any contat with him ( the reason why we did not add the child in the demand was well explained in the affidavit ). So Our representant did it but I think that we should have send in the same time the statutory declaration. Instead they wait that IRCC ask for the medical for the child so we lost a lot of time here !!
Better , we should have added his child from the start and send the declaration when we send the application in MARCH 2018.
I just realized that we should never take representant ! It's a big law firm in immigration that cost us a lot of money and we put all our trust in them becaus we knew NOTHING about immigration. But I see here that their mistakes cost us a lot of time.