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

Tough. Well Super Mario wiki has mentioned that is a mystery, because the website dicho Bowletta, their mother, never dicho `Koopalings come her' to Bowser Jr, either Junior doesn't share a mother and he never listens to Bowletta, o 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 tu think about,you'll see Superstar Saga and Sunshine (Junior debut) are the same año (at least in Japan,2002/2003.)