Is Bowser jr the Koopaling's biological brother of is he their half brother.

Tough. Well Super Mario wiki has mentioned that is a mystery, because the website zei Bowletta, their mother, never zei `Koopalings come her' to Bowser Jr, either Junior doesn't share a mother and he never listens to Bowletta, of his real mother is dead

whos to say that the koopalings werent adopted??? and they are bowser juniors half sibs???dont ask who the mom is.idk

I think (read somewhere) that 'cause of Cackletta's Bowser body possession,an egg was made. It was a side effect of the possession. So,it's probably Cackletta his mother...
If u think about,you'll see Superstar Saga and Sunshine (Junior debut) are the same jaar (at least in Japan,2002/2003.)