Sentence examples for only if they from inspiring English sources

"only if they" is grammatically correct and can be used in written English.
It is typically used to introduce a condition that must be met for something to happen or be true. For example: 1. "I will attend the party only if they play my favorite music." 2. "The project will be successful only if they follow the instructions carefully." 3. "She will forgive him only if they apologize sincerely." 4. "He can go with us on the trip only if they finish their work on time."