Is this sentence correct?

To truly help a patient, I should allow them decide their own choice by letting them hear different life stories.

allow them TO decide

That is not correct.

It should either be:

To truly help patients, I should allow them to decide . . .

Or --

To truly help a patient, I should allow him or her to decide . . .

Yes, the sentence is grammatically correct. However, there is a small error in the phrasing. It should be "To truly help a patient, I should allow them to decide their own choice by letting them hear different life stories."

To determine the correctness of a sentence, it's essential to consider the rules of grammar and syntax. In this case, we can break down the sentence to identify its components:

1. "To truly help a patient" is an introductory phrase that functions as an adverbial clause, providing information about the purpose or condition.
2. "I should allow them to decide their own choice" is the main clause. "I" is the subject, "should allow" is the verb phrase, and "them" is the object. The infinitive "to decide" acts as the direct object of the verb "allow." Finally, "their own choice" is a noun phrase that serves as the direct object of the verb "decide."
3. "By letting them hear different life stories" is a prepositional phrase that acts as an adverbial phrase, providing additional information about the means or method.

So, to determine the correctness of a sentence, it is essential to analyze its components, understand the rules of grammar, and check for proper usage.