So where's their estate meant to be?

Personally I thought that it was meant to be in Tallaght or the surrounding area.

You’re so cool. You’re so cool. You’re so cool.

The place they get off the boat looks like Grand Canal Dock, so I'd put my money on Clondalkin or Tallaght.

In the DVD extras there's an interstitial that identifies it as "Tallaghtfornia". I'm not familiar with Dublin so I don't know if that's the proper full name or if it's a play on words (viz. California) but I think it answers your question.

The estate its recorded in is the Shancastle/Quarryvale area of Clondalkin. Basically across the road from the Arc bar and Clarion Hotel beside Liffey Valley shopping centre