Sentence b is the correct construction: "Which sports is better, soccer or basketball?"
Sentence a is passable but it can be improved by using punctuation, either a comma before the alternatives, "Which sports do you like better, soccer or basketball?", or a colon before the alternatives, " Which sports do you like better: soccer or basketball?"
Sentence c is incorrect because it's a run-on sentence; it needs a comma before the alternatives: "Which sports is better, soccer or basketball?"
As to this question, "Where don't John and Ana check the ball?", it's in the wrong grammatical form. "Shouldn't" should be used instead of "don't" in such sentence constructions, as follows: "Where shouldn't John and Ana check the ball?"
