From what I searched online and my personal experience of inadmissible for PR (not because of security issues but my spouse had a departure order turned into a deportation order. AND my PR application was approved and I got CoPR), RICC will not reject the case by shot gun but through proper procee
1. If CSIS has suspicious, they will need to conduct a interview with the applicant arranged by RICC before finalizing a decision
2. RICC must issue a Procedure Fairness Letter to the applicant about details why they are inadmissible, they must give the applicant a reasonable chance to overcome it within certain amount of time- this was what I received regarding my spouse
As said above, if the three you mentioned got rejected because of security concerns, they muster failed to satisfy CSIS and RICC in the interview and/or with whatever additional information they can provide to ease RICC's concerns. I'm not saying it's going to be easy but it's not like you will get rejected without a chance to fight for it