This is pronounced ben-YUM-in. The 'u' has the sound of the 'u' as in full or pull. Nickname - Yummy, pronounced YUM-mee, same 'u' sound; short second syllable. I've never seen it written in English before. My grandfather, Benjamin, was called by his Hebrew name; I assume it can be spelled other ways as well.

Pronounced bee-nyah-meen. [noted -ed]

Pronounced ben-yah-MEEN or been-yah-MEEN (like many Jewish names, the first syllable is often stressed to sound more casual)
[noted -ed]