We cannot help admiring their effort.
Very unnatural word-for-word translation… There are three problems in the original Japanese sentence.
努力には is a wrong use of particle. It also sounds redundant to repeat には twice (努力には & しないわけには).
“Can’t help doing” is often translated as ～しないわけにはいけない or ～せざるを得ない. But this typical translation by dictionaries sounds unnatural.
賞賛する means “to be worth to give a monetary prize”. 賞賛する is not used in the context of reputation and acclaim. 称賛する (also pronounced as しょうさんする) is the right Kanji. For more details, please read this article.
My alternative translation is:
彼らの尽力は大いなる称賛に値する。（かれらのじんりょくはおおいなるしょうさんにあたいする）= (lit,) Their effort (and contribution) should be highly acclaimed.
Both 努力 and 尽力 are translated as “efforts”, but 努力 is mainly used for one’s personal effort whereas 尽力 is closer to “devotion” and “contribution” (i.e. not only for one’s sake but also for others).
称賛に値する is a common set phrase. Just memorize it.