The phrase "are required not only" is correct and usable in written English.
It is typically used to indicate that there are multiple requirements or conditions that must be met, often followed by "but also" to introduce additional requirements.
Example: "Employees are required not only to complete their tasks on time but also to collaborate effectively with their team members."
Alternatives: "must not only" or "are obligated not only".
Approvals are required not only by the commission but also by the local architectural review board.
The rules say the inspectors are required not only to detail violations in their reports, but also to specify how the violations should be corrected.
First mounted at the Sydney Opera House in 1990, Mr. Luhrmann's "Bohème" is set in 1957 Paris and has been specifically cast with young, good-looking performers who are required not only to sing but also to act.
However, to realize such benefits, efforts are required not only in the selection of appropriate technologies but also in the choice of proper materials.
Deriving high quality daily rainfall estimates are required not only for successful hydrological modelling but also for its application in ungauged basins.
Additionally, a stable conformation and rigid cytoskeleton are required not only for the formation of a transmembrane transducer but also for P-selectin-induced calcium signaling.
This was my education and the behaviour was required not only in the funeral home but anywhere, at any time.
The pairings were required not only to find the correct answer, but to explain why all of the other options were wrong.
They were required not only to write official poetry but also to instruct the residents of the area in law, literature, and national history.
Gramercy is one of two private parks in New York City (the other, in Queens, is Sunnyside Gardens Park), and a key is required not only to enter, but to leave through a gate in its wraparound wrought-iron fence.
But because cabs were required not only to recalibrate their meters but also to update their external markings before charging the new fare, any cab with the old markings should, theoretically, be charging the old fare.
