Thats right, you would have to have completed 18 months before you could apply for child benefit. The applicant should have stayed for 18 months and they usually recommend your spouse (in case of not working) to be the primary applicant so that you could save some tax. So, if you are going to have your wife to be the primary applicant then she would have to stay for 18 months before she could apply for the benefit.
Yes, I believe they would have to wait for 3 months before getting the coverage, looks like you are in BC (Vancouver??), you would have to send an application form with the copy of your WP along with the landing papers of all the family member, hence, you cannot get the medical coverage for the whole family without getting them here, you will have to get it first, then once they land here, add them as additional family members along with you.
Good luck.