Instinctively I would pronunce it like the French name
Jean but with two syllables, like zhe-an. But I think it's supposed to be the same as
Jean in French.
In English I wouldn't pronounce it like
Jean, but I wouldn't pronounce it Jeen-ee either. The "-nne" suffix wouldn't make sense for "nee" IMO. Maybe je-ann or something beterrn jeen and jee-ann?