I am sorry for the delay - I was trying to see a way through this for you without starting divorce proceedings.
Unfortunately there is not.
There is no way that you can prevent your husband bringing his child to the UK.
He can also bring him to the house whenever your husband himself is in the house (although legally you could make him take the child with him every time he does out)
The only way that you can make it clear that the child will not live with you and your daughter as a family is to start Divorce proceedings.
This need not be expensive
The process is described here
You may be eligible for help with the £550 fee - that is why I asked about your income
I am sorry for the length of time this took - it is hard sometimes to try and get enough informtaion to look at all the options.
Please ask if you need further details, or still wish a refund.