Company's Mission & Vision Statement

How am I going to make a company\'s mission and vision statement if it\'s a group of companies with different nature of business? This information will be used in the establishment of our company manual

You can't do it on your own. Usually, for progressive companies, it is the CEO and the Management Board who decides on the mission and vision of the company.

You can't do it alone.
It has to be driven by the CEO of the company. In this case, many CEOs or the biggest boss in the different business to come together to brainstorm and agree collectively a shared-vision.
Even if you are able to get this group of heavy weights together, it is best you engaged an experienced external consultant to facilitate to session.
As there are many businesses with different business nature, you may have to spend a substantial amount of time i.e. over a few months to finally arrived at a shared vision.
Autumn Jane

the person that should be doing this is the CEO or the "big guys of the company."
but if you are tasked to really do this, buy a strategic management book. there are rules there. make sure that you know the core values of the company. you have to harmonize your vision statement with that.