The phrase "most longstanding and" is grammatically correct and usable in written English.
It is typically used to introduce a quality or characteristic that has been present for a long time. Example: "The most longstanding and well-respected tradition of the town is the annual summer festival."
Marriage, however flawed, is the most longstanding and effective means of encouraging monogamy in our society.
Mr. Obama is a man with many mentors, but she has been one of his most longstanding and influential tutors, navigating him through Chicago civic and political circles.
One of our most longstanding and enthusiastic supporters, Mr. Hannan made numerous outstanding contributions to ensure the health of our Hospital and its patients for more than half a century.
Get a fix of the "holy trinity" of grilled chicken (gai yang), sticky rice (khao niew) and grated vegetable salad (som tum) at Nomjit Gai Yang (corner of Ekamai Soi 18), one of the neighbourhood's most longstanding and well-regarded vendors of Isaan cuisine.
Disney's female heroines and villainesses stand proudly amongst the most longstanding and beloved fictional characters -- both online and off.
Former Native American lands in the watershed were taken over by settlers, leading to some of the most longstanding and violent wars against indigenous peoples in American history.
But she is tired of being the town's most longstanding fiancée, and wonders when he will mention a date for the wedding.
But The Rich Forks has been Van's most longstanding project and next week a small amount of them will be exhibited at a community arts centre in Melbourne before the collection travels the world.
Winston Churchill's grandson, one of Parliament's most longstanding Eurosceptics and a deputy Speaker of the Commons have all been recognised in the Queen's Birthday Honours List.
As an artist, Maliphant's closest and most longstanding creative partner is lighting designer Michael Hulls, who has worked with Maliphant since 1994, and whose lighting is as integral as the choreography to both the creation and the performance of Maliphant's work.
But Maria's deepest and most longstanding attachment was to Tennessee Williams.
