In the following questions, few sentences are given. Choose and mark the sentence which contains no grammatical or contextual error in it. If all the sentences are grammatically and contextually incorrect, mark "All are incorrect" option as the answer choice.

The correct option is "He admitted to forging the signature on the lease agreement knowingly."

Step-by-step breakdown and grammatical analysis:

1. "She would rather to forfeit her claim than drag the dispute into litigation."
Grammatical Error: The phrase "would rather" is followed by a bare infinitive (infinitive without "to"). Therefore, using "to forfeit" is incorrect.
Corrected Sentence: "She would rather forfeit her claim than drag the dispute into litigation."

2. "The magistrate along with his clerks were seated when the hearing resumed."
Grammatical Error: When two subjects are connected by "along with", the verb agrees with the first subject ("The magistrate", which is singular). Therefore, the plural auxiliary verb "were" should be replaced by the singular verb "was".
Corrected Sentence: "The magistrate along with his clerks was seated when the hearing resumed."

3. "He admitted to forging the signature on the lease agreement knowingly."
Analysis: The verb "admitted" correctly takes the prepositional construction "admitted to" followed by a gerund ("forging"). The sentence is grammatically sound, well-structured, and contextually precise.

4. "Every one of the cadets are obligated to report at dawn for physical training."
Grammatical Error: The subject of the sentence is "Every one", which is singular. Thus, it requires the singular verb "is" rather than the plural verb "are".
Corrected Sentence: "Every one of the cadets is obligated to report at dawn for physical training."

Thus, the third sentence is the only one without any grammatical or contextual errors.