"Their help is very helpful."
Translation:Bantuan mereka sangat membantu.
'membantu' is a verb, the English translation is an adjective.
I think there is no other way to translate this with a verb in English.
Well, at least, I don't know which verb to use, and how to use it in English.
"Their help is helping"….this is weird, this doesn't work.
How about: "Bantuan mereka sangat bermanfaat."
I don't know if it's an accepted translation.
'bermanfaat' = useful, beneficial, advantageous
It seems to me that the mem+bantu would demand an object (siapa) which is absent here.
Yes, 'membantu' is a transitive verb.
With some transitive verbs, the object is optional (semitransitif).
Examples semitransitif (object is optional):
5a1) Tini menyapu. (S-P)
5a2) Tini menyapu rumah. (S-P-O)
5b) Rumah disapu oleh Tini.
6a1) Tini sedang membaca. (S-P)
6a2) Tini sedang membaca buku. (S-P-O)
6p) Buku sedang dibaca oleh Tini.
These are examples from this grammar topic:
Transitive & Intransitive verbs, Tips & notes, Addendum.
'membantu' is semitransitif (object is optional).