Actually, you can support The Stevens if “The Stevens” is a single thing, like a museum or an orchestra. “The Clark.” “The Philharmonic.”
But in this case, we’re talking about the Stevens family. You can support the Stevens family, or you can support the Stevenses, but in English, you can’t support the Stevens.
My friends the Evanses have this same problem. As do the Jameses, the Edwardses, the Gosses….
(Wait. If you had a bunch of guys named Steven, you could support all of them. Then you would be supporting the Stevens.)