Hello Richard
I've not been able to find a marriage for them in Dudley, which is the registrations district for Sedgeley. There was a John Wright married to a Sarah Hill in 1879 in Dudley, but I'm fairly sure that wasn't them, because on the 1881 census John is lodging in Walsall - he is a Puddler, born Sedgeley - and he is unmarried.
In order to pin down a possible marriage in another registration district, therefore, I think you will need one of the children's birth certificates to find Sarah's maiden name.