They've been referred to as Bert and Ernie from literally the moment that Alfie and Kat discovered they were expecting twins, that's where the rumours came from... the show itself started them. Some people repeated the names and then people who hadn't picked up on it in the show itself started to think they were going to be the actual names.
I can see Kat warming to Albert and Ernest, but it doesn't really go with Tommy. I think we'll have something completely different.