I'm extremely upset with myself because I was in charge of all the sponsorship/immigration forms, and we forgot to fill out the IMM5406 Additional Family info form.

So here's the issue...
My husband (the person I'm sponsoring) has half-siblings but he doesn't even know them. Is it really necessary to include them? He doesn't even know their names let alone their birthdates or anything. He doesn't even know if they're still alive. What should we do?