You don’t indicate the form of entity of your foundation. If it is a corporation, some states require a minimum of three directors (or trustees), but other states permit a single director to govern. A trust would not normally require more than one trustee. 

 

The IRS has no requirement for a minimum number of directors or trustees but may be hostile and ask a lot of questions if you seek to convert with only you and your wife on the Board. By giving notice of your intent to qualify as a public charity, you can usually get an advanced ruling to remove your existing entity from the private foundation classification. It is probably unnecessary to start a new entity in order to qualify under IRS rules.