Identical Irish twins Shane and James Duncan live in New York and London, respectively, so seeing them together at their parents' home in Ireland is a rare occurrence. So using their mother's complete ignorance that they were both in town, the twins decided to play a trick on her.
Anne thinks she's talking to James, who's helping her fix something in the backyard. Until James emerges from the house carrying a toolbox and Anne suddenly realizes (with a little NSFW language) that she'd been talking to Shane the whole time.
The guys had switched clothing at some point after Shane arrived at the house so Anne would have no idea the man she thought was James had actually turned into Shane. When she sees them at the same time, she's understandably floored.
The joke is revealed within the first 30 seconds of the video; the other minute and a half is just Anne hugging her son and not letting go, because that's how moms are. Oh, moms—please never change. Not that y'all were planning to.