I did not see your message, sorry .

I called Air Canada sometime late afternoon in North America and was told that Toronto Airport would handle the connections, including any needed rebookings, as it was too early to figure out whether they would actually be able to get on or not. And, I was told that they were aware of non-English speaking passengers on that flight. Upon landing, my relatives were told that they have to stay overnight in Toronto, was taken through the Canadian immigration, filed for customs since bags did not come out, and given hotel and meal vouchers. My friend in Toronto was expected them in the Arrival Hall (I had Air Canada called him in case of flight mis-connect and Air Canada did) and taken from there. All were smooth. They arrived Houston the next day. It looks like I was worrying too much.

With these said, I assume the kind of compensation (Notice of Denied Boarding Compensation - EU Member Countries) that I got last summer for my delayed flight last summer (Notice of Denied Boarding Compensation - EU Member Countries) was an European thing and only applies for Canada <> EU flights and does not apply in this case, for which my relatives arrived with an even longer delay.

Thank you all for your advice, though, they did help a lot in this case in giving me idea what should be done. It is the first time that my family travelling solo like this - I used to live in Toronto and could travel with them.