dui questions

Hi,
I have a few questions regarding dui's and I thought maybe some people here would have knowledge or perhaps experience. I don't because they're not mine *phew* .. I'm getting married soon in Canada and my family wants to join me for the occasion, unfortunately one of my brothers and my dad have very old dui's. My dad's is from 26 years ago and my brother's is from 15 years ago (he was 17 when it occurred, so I'm not sure the rules regarding that either). I was just wondering what the best steps for them would be as far as ensuring they will be able to come to the wedding. I was reading that they can be deemed rehabilitated as they have had no other offenses since then, and the offenses they do have were more than 10 years ago. Basically I am just looking for information on the best way to go about being deemed rehabilitated. Do they need to go to the border and specifically request this? I expect they're going to try and get this taken care of before the weekend of the wedding so they wouldn't actually be wanting to get into Canada, can they go to an immigration office instead or must they go to a border crossing? Anything else I should be thinking about?

Thanks,
imp