Ah, so he is pursuing a property settlement against you. Now I understand.
So, the court follows a four-step process when deciding a property settlement:
1. What is the value of the joint asset pool?
2. What were the financial and non-financial contributions of each party?
3. What are the future needs of each party?
4. Is the settlement just and equitable?
For de facto relationships, the rules are slightly different - if your relationship was relatively short, then the court will endeavour to ensure each party maintains the assets they had prior to entering into the relationship. Thus, if you had the house before commencing the relationship, and the relationship was anywhere less than, say, a few years in length, then you stand a much greater chance of holding on to the house you already owned. This is heightened further because you have a future need to care and provide shelter for a child.
The court requires full and frank disclosure of all assets involved in a property settlement, but if he has not disclosed his investment in the house his brother now owns, then you may wish to provide whatever evidence you have of his contribution to the house. If you wish, you can also subpoena bank records relating to mortgage repayments. Bear in mind, of course, that this will need to be considered as a joint asset, if considered part of the asset pool, so you will need to include it in your evidence constructively, such as seeking a settlement whereby he keeps that house, and you keep your house. Basically, you want to be showing that both houses should be considered as part of the joint asset pool, rather than just your house. Thus, it's not prudent to argue that 'I don't want any of it, I just want to show it exists', but rather that 'I want a portion of the joint asset pool by keeping the house I own'. Does that make sense?
Anyway, I hope this helps.