Absolutely Do Not accept it. Refuse to come until they promise what was in your initial contract/agreement. It's a common ruse they use all the time.
If it's an internal mistake or policy change that's not your problem and that's not what was agreed.
I know you don't want to rock the boat with a new job but they are doing you over before you join. You have some bargaining power at the moment. Use it. Once you're here you have none.
As said above, your wife will be unhappy and it's not gonna get any better once you're here. Joining now, in summer in an apartment she's gonna go stir crazy down there.
Cannot stress enough, don't get on the plane till it's in writing.
Get angry....they don't like that in HR!!
They will change it as they know they are in the wrong. It's been done before.
Good luck.