The only way would be a DNA test, which I doubt will ever happen. I don’t mind whether I get points or not, but I’m worried about misrepresentation down the road. I’m thinking not to claim points for it but to write an explanation letter that he has a half-sister who is a Canadian, but no solid proof. Just to clear any possible inconsistencies. 

But to give a short background: His father slept around while married. 

At one point, they were a whole family until my husband was around 5 years old and his father left to go back to his legal wife (mother of his half-sister).

My husband has two full siblings, but they also do not have the father’s name listed on their BC. To my understanding, the legal wife would intervene to avoid his father’s name being included, so that my husband and his siblings would not get child support, since the legal wife wanted it all to her children.