'Is being' signifies at this moment. If you say 'He is helpful', that's a general comment and does not describe his behaviour now. You can actually say 'He ıs being sick'! That means he is vomiting. :) In all your cases, these are active sentences in present continuous. A passive example would be, 'He is being helped'. (Note the participle: helped.)

Your question is why do we use the "present continuous" (also called "present progressive") and not just the present ? The present continuous is used when emphasizing a temporary event or the temporary duration of an action. Example: "The film is starting now." or " I'm getting nervous." If you say, "He is sarcastic." or "He is a sarcastic person," the implication is that this is a permanent trait or attribute of this person. If you say, "He IS (just) BEING sarcastic," it implies that only at this moment in time is he acting sarcastically. He is not always like this. "Is she always like this?" "No, she's just being silly." or "Yeah, she's a silly girl."