Yes, but I would prefer "there are" to "there's", although you will hear the latter.
Can this be said:
The reason why I got us together is because between the four of us we speak four different languages and that means there's four different markets we could penetrate.
Does it make sense?
You don't need "why" after "reason".
Remember - if you don't use correct capitalisation, punctuation and spacing, anything you write will be incorrect.