Basically replace the members of the Star family with a Nicktoon character. My idea was:
Jimmy Neutron replaces Squidina in Rock Bottom.
Timmy Turner replaces Cecil in Ripped Pants.
Danny Phantom replaces Bunny in Neptune's Spatula
Invader Zim replaces GrandPat in Help Wanted
Lincoln Loud replaces Granny Tentacles
(Ignore the fact none of them can breathe underwater naturally.)