Visas – Canadian Parents Staying 8 Months in the United States

I live in the United States with a green card. My father retired and my mother had a year off (until September). We are all Canadian citizens.

I just had a child and they wanted to come visit me and stay with me until the end of August to become grandparents. I know that as Canadians, you have 182 days without needing a visa, but I have a hard time finding the options that they offer to them (for example, staying 8 months instead of 6). In the worst case, of course, they can come back sooner. I think we should apply for a B2 visa, but I have not found a concrete answer