Any advice on how to find long lost family?

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When I was 12 my brother's girlfriend packed up their 3 kids and ran off while my brother wasn't home. My mom, who was devastated, hired a PI to find where they had gone. We found them in Calgary, Alberta and took a trip there to pay them a surprise visit. Let's just say she was surprised to see us. She let us take the kids for the afternoon and we took them to Chucky Cheese. After a few hours, we reluctantly returned the children to their mother. Then we made the trip back to BC. The final report(the last one my mother could afford) from the PI said that she had almost immediately packed up and moved with the kids, address unknown. It's been over 18 years. I am now an adult with 2 kids of my own and the 3 kids (2 boys and 1 girl) are all adults now, too. Now that they are old enough that their mother has no say in who they do and do not know, I am very interested in tracking them down, not just to get to know them, but to warn them about genetic health issues that they can prevent if they know about them. I know very little about them, and to make it even harder, they have very common names of which I do not know the middle names. And my mother, the one person who had the information, has since passed on. So far I have tried looking in phonebook listings(overwhelming) and tried a search on facebook(no luck). So I implore you, myLotters, to let me know of any FREE methods of looking for people. Specifically in Canada. At this time I haven't got the money to pay for any kind of search. Thanks everybody