Technically they need to have lived together for 1 continuous year and be able to prove it. With her time in a Italy it seems like they don’t qualify for common law. Some may try and show the evidence they have to the airline, sometimes people get lucky. If you live in Manila getting to the airport and trying is not a big deal but if you fly to Manila and get rejected getting back to your home may be very difficult and so that needs to be considered. The cost of the flight and whether you will get a refund if you are denied boarding is another issue that needs to be factored in.
I think we are both on the same page now. Getting to MNL and being denied boarding is not fun, I can attest to that first hand because we are in that position right now. One week ago we managed to get to MNL only to have PH Immigration tell my wife and son they couldn't leave the country, there is a ban on PH citizens leaving the country if on a tourist visa. We have a PR application in process and were going to enter under dual intent.
But the part of the experience that more applicable in this situation is convincing the airline when you check in that you are qualified to enter. The agent insisted that we couldn't, I knew they could as far as Canada is concerned. They got the CDN embassy on the phone. We had our marriage certificate and my son's Birth certificate to show them, The embassy confirmed they could enter.
Lacking some kind of document saying they are common law is the problem and I am not aware that any official government exists? If they want to stay together I suggest they stay where they are and not try right now.
We are stuck in MNL until PH immigration relaxes the rules for us to go to Canada or they resume domestic flight here for us to go back to our home here. We were flying with ANA who promptly refunded our ticket with 1 phone call. Other airlines might not be so easy to deal with for a refund.