Firstly tell us exactly the type of event and audience you need the interpreters for, so that we can advise which is the best type of of intepreting and provide the most suitable interpreters.
Bear in mind that interpreters work 20 minutes on and 20 minutes off, so you always need 2 interpreters, unless it is an informal situation or a brief meeting. Interpreting, expecially simultaneous interpreting is very demanding and requires a lot of skill and most of all concentration.