They're so used to it, that they sit and talk to each other like friends, and between words bowser tries to convince her to marry him and get an DNA test with the koopalings. All that while they wait for Mario to come. He goes "Woo-hoo" and "Yahoo" a couple of times and everybody knows the rest...
There's no need to put it like that guys. I think everybody(including me) who said things like that where joking.
As for the koopalings, i don't think Nintendo will ever reveal that.
Sorry for going off- topic.