grammatical number - Apostrophes and caps in Happy Mother’s Day / Happy Mothers’ Day

So, I’m writing this as it is Mother’s (or maybe Mothers’) Day today, and I was wondering what would be a correct way to write that.

Should the apostrophe come be between the r and the s, or after the s?

And are the following capitalization correct?

Happy Mother’s (or Mothers’) Day!

and

I wish you a Happy Mother’s (again, maybe Mothers’) Day!

and also

I sure spent a nice Mother’s (maybe Mothers’) Day with my momma!