Hi, that's a crap contract.

1. Employment for only half a year? Sounds fishy. Well, if they don't have enough students, they will kick you out like that in the street. Not nice!
2. Probationary period of 1 month for such a short period of six months in total? Crazy. It means they will pay you less in the first month, and that's crap! Give these idiots a miss! That also means they can kick you out any time before when it suits them! ---Pphhhew!!!!
3. Holidays/Vacation; it seems you have practically none, they want to use you any time at the convenience of their students. What a f..ck!

There is another crap online business called Web International; it is has been discussed here before. Sounds very much like them.
I can tell you right now from these few things: That's a crap job offer, decline it and give these fools a miss. Look somewhere else instead!